Refactor(api): Convert biometricAuthAvailable and deleteKeys to asynchronous calls

Updates the `BiometricSignatureApi` to use callback-based (Android) and completion-based (iOS/macOS) asynchronous patterns for `biometricAuthAvailable` and `deleteKeys`. This ensures consistency across the plugin's native implementations and aligns with Pigeon's asynchronous messaging requirements.

- **Android**: Updated `biometricAuthAvailable` and `deleteKeys` to accept a `Result` callback.
- **iOS/macOS**: Refactored `biometricAuthAvailable` and `deleteKeys` to use `@escaping` completion handlers instead of synchronous return values.
- **Pigeon**: Updated the generated API glue code to handle the asynchronous message flow for these methods.

Author: chamodanethra

android/src/main/kotlin/com/visionflutter/biometric_signature/BiometricSignaturePlugin.kt

@@ -95,15 +95,16 @@ class BiometricSignaturePlugin : FlutterPlugin, BiometricSignatureApi, ActivityA
 
     // ==================== BiometricSignatureApi Implementation ====================
 
-    override fun biometricAuthAvailable(): BiometricAvailability {
+    override fun biometricAuthAvailable(callback: (Result<BiometricAvailability>) -> Unit) {
         val act = activity
         if (act == null) {
-            return BiometricAvailability(
+            callback(Result.success(BiometricAvailability(
                 canAuthenticate = false,
                 hasEnrolledBiometrics = false,
                 availableBiometrics = emptyList(),
                 reason = "NO_ACTIVITY"
-            )
+            )))
+            return
         }
 
         val manager = BiometricManager.from(act)
@@ -118,12 +119,12 @@ class BiometricSignaturePlugin : FlutterPlugin, BiometricSignatureApi, ActivityA
 
         val reason = if (!canAuthenticate) biometricErrorName(canAuth) else null
 
-        return BiometricAvailability(
+        callback(Result.success(BiometricAvailability(
             canAuthenticate = canAuthenticate,
             hasEnrolledBiometrics = hasEnrolledBiometrics,
             availableBiometrics = types,
             reason = reason
-        )
+        )))
     }
 
     override fun createKeys(
@@ -440,9 +441,9 @@ class BiometricSignaturePlugin : FlutterPlugin, BiometricSignatureApi, ActivityA
         }
     }
 
-    override fun deleteKeys(): Boolean {
+    override fun deleteKeys(callback: (Result<Boolean>) -> Unit) {
         deleteAllKeys()
-        return true
+        callback(Result.success(true))
     }
 
     override fun getKeyInfo(checkValidity: Boolean, keyFormat: KeyFormat, callback: (Result<KeyInfo>) -> Unit) {

ios/Classes/BiometricSignaturePlugin.swift

@@ -130,7 +130,7 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
 
     // MARK: - BiometricSignatureApi Implementation
 
-    func biometricAuthAvailable() throws -> BiometricAvailability {
+    func biometricAuthAvailable(completion: @escaping (Result<BiometricAvailability, Error>) -> Void) {
         let context = LAContext()
         var error: NSError?
         let canEvaluate = context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)
@@ -149,12 +149,12 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
 
         let hasEnrolled = error?.code != LAError.biometryNotEnrolled.rawValue
 
-        return BiometricAvailability(
+        completion(.success(BiometricAvailability(
             canAuthenticate: canEvaluate,
             hasEnrolledBiometrics: hasEnrolled,
             availableBiometrics: availableBiometrics,
             reason: error?.localizedDescription
-        )
+        )))
     }
 
     func createKeys(
@@ -361,9 +361,9 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
         }
     }
 
-    func deleteKeys() throws -> Bool {
+    func deleteKeys(completion: @escaping (Result<Bool, Error>) -> Void) {
         deleteExistingKeys()
-        return true
+        completion(.success(true))
     }
 
     func getKeyInfo(checkValidity: Bool, keyFormat: KeyFormat, completion: @escaping (Result<KeyInfo, Error>) -> Void) {

macos/Classes/BiometricSignatureApi.swift

@@ -761,7 +761,7 @@ class BiometricSignatureApiPigeonCodec: FlutterStandardMessageCodec, @unchecked
 /// Generated protocol from Pigeon that represents a handler of messages from Flutter.
 protocol BiometricSignatureApi {
   /// Checks if biometric authentication is available.
-  func biometricAuthAvailable() throws -> BiometricAvailability
+  func biometricAuthAvailable(completion: @escaping (Result<BiometricAvailability, Error>) -> Void)
   /// Creates a new key pair.
   ///
   /// [config] contains platform-specific options. See [CreateKeysConfig].
@@ -785,7 +785,7 @@ protocol BiometricSignatureApi {
   /// [promptMessage] is the message shown to the user during authentication.
   func decrypt(payload: String, payloadFormat: PayloadFormat, config: DecryptConfig?, promptMessage: String?, completion: @escaping (Result<DecryptResult, Error>) -> Void)
   /// Deletes keys.
-  func deleteKeys() throws -> Bool
+  func deleteKeys(completion: @escaping (Result<Bool, Error>) -> Void)
   /// Gets detailed information about existing biometric keys.
   ///
   /// Returns key metadata including algorithm, size, validity, and public keys.
@@ -802,11 +802,13 @@ class BiometricSignatureApiSetup {
     let biometricAuthAvailableChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.biometric_signature.BiometricSignatureApi.biometricAuthAvailable\(channelSuffix)", binaryMessenger: binaryMessenger, codec: codec)
     if let api = api {
       biometricAuthAvailableChannel.setMessageHandler { _, reply in
-        do {
-          let result = try api.biometricAuthAvailable()
-          reply(wrapResult(result))
-        } catch {
-          reply(wrapError(error))
+        api.biometricAuthAvailable { result in
+          switch result {
+          case .success(let res):
+            reply(wrapResult(res))
+          case .failure(let error):
+            reply(wrapError(error))
+          }
         }
       }
     } else {
@@ -895,11 +897,13 @@ class BiometricSignatureApiSetup {
     let deleteKeysChannel = FlutterBasicMessageChannel(name: "dev.flutter.pigeon.biometric_signature.BiometricSignatureApi.deleteKeys\(channelSuffix)", binaryMessenger: binaryMessenger, codec: codec)
     if let api = api {
       deleteKeysChannel.setMessageHandler { _, reply in
-        do {
-          let result = try api.deleteKeys()
-          reply(wrapResult(result))
-        } catch {
-          reply(wrapError(error))
+        api.deleteKeys { result in
+          switch result {
+          case .success(let res):
+            reply(wrapResult(res))
+          case .failure(let error):
+            reply(wrapError(error))
+          }
         }
       }
     } else {

macos/Classes/BiometricSignaturePlugin.swift

@@ -144,7 +144,7 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
 
     // MARK: - BiometricSignatureApi Implementation
 
-    func biometricAuthAvailable() throws -> BiometricAvailability {
+    func biometricAuthAvailable(completion: @escaping (Result<BiometricAvailability, Error>) -> Void) {
         let context = LAContext()
         var error: NSError?
         let canEvaluate = context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)
@@ -163,12 +163,12 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
 
         let hasEnrolled = error?.code != LAError.biometryNotEnrolled.rawValue
 
-        return BiometricAvailability(
+        completion(.success(BiometricAvailability(
             canAuthenticate: canEvaluate,
             hasEnrolledBiometrics: hasEnrolled,
             availableBiometrics: availableBiometrics,
             reason: error?.localizedDescription
-        )
+        )))
     }
 
     func createKeys(
@@ -255,9 +255,9 @@ public class BiometricSignaturePlugin: NSObject, FlutterPlugin, BiometricSignatu
         }
     }
 
-    func deleteKeys() throws -> Bool {
+    func deleteKeys(completion: @escaping (Result<Bool, Error>) -> Void) {
         deleteExistingKeys()
-        return true
+        completion(.success(true))
     }
 
     func getKeyInfo(checkValidity: Bool, keyFormat: KeyFormat, completion: @escaping (Result<KeyInfo, Error>) -> Void) {