Use native CLGeocoder in geocoding_darwin example

[rickdijk]

Summary

• Refactors the geocoding_darwin example to use the native CLGeocoder API via clgeocoder.dart instead of GeocodingDarwinFactory / the shared Geocoding interface.
• Aligns with how the geocoding_android example demonstrates its native Geocoder API.

Test plan

• cd geocoding_darwin/example && flutter run
• Run example on iOS or macOS and verify reverse/forward geocoding and locale selection

[Copilot]

Pull request overview

Refactors the geocoding_darwin example app to demonstrate the native Darwin geocoding surface (CLGeocoder) directly via clgeocoder.dart, mirroring the platform-native style shown in the Android example.

Changes:

• Replaces usage of GeocodingDarwinFactory / Geocoding with direct cl.CLGeocoder calls.
• Adds async handlers for forward/reverse geocoding with basic error handling (PlatformException, FormatException).
• Updates display helpers to format CLPlacemark and CLLocation results (including coordinate/timestamp retrieval).

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[mvanbeusekom]

The new implementation of the example/lib/main.dart is exactly how I envisioned it.

The only thing I didn't mention (and is also not mentioned in the CONTRIBUTING.md guide) is that each PR:

1. Should only apply to one specific package (which is the case for this PR, as it only affects the geocoding_darwin package).
2. Should update the version in the pubspec.yaml and a matching entry in the CHANGELOG.md file.

You did create an entry in the CHANGELOG.md (which uses the correct style), but it should contain a new version number and this new version number should also be updated in the pubspec.yaml file.

[mvanbeusekom]

You can directly create a new version number and use it here (can be a patch fix, so I suggest using version 1.0.1).