Fixes #45.

Summary

• thin the bundled iOS simulator dylib per target architecture in the Flutter native-asset build hook
• emit an architecture-specific simulator asset instead of returning the same fat dylib for both arm64 and x86_64 targets
• add a changelog entry for the Flutter package

Why

The current hook returns native_libraries/ios-sim/vector_ios-sim.dylib for every iOS simulator target. That file already contains both simulator architectures, so Flutter can end up trying to combine duplicate fat inputs during code asset packaging and fail with a lipo error.

Verification

• reproduced the failure in a Flutter app using sqlite_vector on iOS simulator builds
• verified locally that thinning the simulator dylib per architecture fixes the packaging failure
• ran dart pub get && dart analyze in packages/flutter

dart analyze reports two existing informational lints unrelated to this change:

• unnecessary_library_name in lib/sqlite_vector.dart
• non_constant_identifier_names in lib/src/sqlite_vector.dart