fix(geocoding_darwin): declare pigeon as a dev_dependency

[bjrochem72]

Moves pigeon from dependencies to dev_dependencies in geocoding_darwin.

Pigeon is a build-time code generator. The generated lib/src/geocoding/geocoding.g.dart is self-contained and doesn't import package:pigeon at runtime, so it doesn't need to be a runtime dependency. geocoding_android already declares it under dev_dependencies; this just brings geocoding_darwin in line.

Because it's a regular dependency today, pigeon is pulled into every app that depends on geocoding, and pigeon's analyzer >=10.0.0 <13.0.0 constraint then caps the whole app's analyzer at 12. That blocks any package in the app that needs analyzer 13+. In our project it prevents upgrading riverpod_generator/riverpod_lint (3.4+) and drift_dev, which all require analyzer ^13, and there's no workaround short of dropping geocoding since it's the only path pulling pigeon in.

Fixes#304.

Verification:

• grep -rn "package:pigeon" geocoding_darwin/lib returns nothing (no runtime use).
• flutter pub get in the example app still resolves.

[bjrochem72]

@mvanbeusekom would you be able to review this one? It's a two-line move of pigeon to dev_dependencies in geocoding_darwin to match geocoding_android — the CHANGELOG and version bump (1.0.3) are included. As covered in #304 it currently leaks pigeon's analyzer <13 ceiling into every app using geocoding 5.x, and it isn't fixable downstream. A geocoding_darwin 1.0.3 release afterwards would be much appreciated.

[mvanbeusekom]

Good catch, thanks for the contribution.