- Add environment variable-based permission defines (PERMISSION_CAMERA, etc.)
- Allow consumers to selectively enable only needed permissions
- Default all permissions to 0 (disabled) for minimal footprint
- Keep essential header search paths
- Simplified structure without unnecessary framework dependencies

Based on approach from Baseflow#1440

- Move source files to SPM-compliant structure (ios/permission_handler_apple/Sources/)
- Add Package.swift with environment-based permission defines
- Update podspec to reference new file locations
- Add GitHub workflow matrix testing for both CocoaPods and SPM
- Maintain backward compatibility with existing CocoaPods setup

Follows on Baseflow#1440 and fixes Baseflow#1439