fix(auth): resolve format string mismatch in ASF timestamp generation (#4095)

Fixes #4073

Changed timestamp generation in CognitoUserPoolASF.prepareJsonPayload to use Int64 instead of Double to match the %lli format specifier. This resolves the format string mismatch warning that was appearing during sign-in operations.

The issue was caused by floor() returning a Double while the format string expected an Int64. Converting directly to Int64 maintains the same functionality while eliminating the type mismatch.

Author: harsh62

AmplifyPlugins/Auth/Sources/AWSCognitoAuthPlugin/ASF/CognitoUserPoolASF.swift

@@ -86,7 +86,7 @@ struct CognitoUserPoolASF: AdvancedSecurityBehavior {
         contextData: [String: String],
         userPoolId: String
     ) throws -> String {
-        let timestamp = String(format: "%lli", floor(Date().timeIntervalSince1970 * 1_000))
+        let timestamp = String(format: "%lli", Int64(Date().timeIntervalSince1970 * 1_000))
         let payload = [
             "contextData": contextData,
             "username": username,