feat(BILL-252): Add iOS Simulator arm64 support (#71)

## Summary
Add support for Apple Silicon iOS simulators by properly detecting
simulator targets and selecting the correct CouchbaseLite framework
variant.

## Solution
The fix checks the full `TARGET` environment variable for `"sim"` or
`"x86_64"` to determine if it's a simulator build, and selects the
appropriate framework:
- **Device** (aarch64): `ios-arm64`
- **Simulator** (aarch64 or x86_64): `ios-arm64_x86_64-simulator`

## Testing
- ✅ Builds successfully for `aarch64-apple-ios-sim` target
- ✅ Existing `x86_64-apple-ios` simulator builds still work
- ✅ Device builds (`aarch64-apple-ios`) unaffected

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude <[email protected]>

Author: EliseChouleur

build.rs

@@ -210,9 +210,11 @@ fn configure_rustc() -> Result<(), Box<dyn Error>> {
     let target_os = env::var("CARGO_CFG_TARGET_OS")?;
     if target_os == "ios" {
         let target_arch = env::var("CARGO_CFG_TARGET_ARCH").expect("Can't read target_arch");
-        let ios_framework = match target_arch.as_str() {
-            "aarch64" => "ios-arm64",
-            "x86_64" => "ios-arm64_x86_64-simulator",
+        // Check if this is a simulator target by looking at the full TARGET string
+        let is_simulator = target_dir.contains("sim") || target_dir.contains("x86_64");
+        let ios_framework = match (target_arch.as_str(), is_simulator) {
+            ("aarch64", false) => "ios-arm64",
+            ("aarch64", true) | ("x86_64", _) => "ios-arm64_x86_64-simulator",
             _ => panic!("Unsupported ios target"),
         };