[Enhancement proposal]: Add SPM Support

[engels-all-win-software]

Please check the following before submitting a new issue.

• [x] I have searched the existing issues.
• [x] I have carefully read the documentation and verified I have added the required platform specific configuration.

Please select affected platform(s)

• [ ] Android
• [x] iOS

Proposal

Since Flutter is now moving forward to support SPM in order to deprecate CocoaPods, implementing SPM in advance for flutter-geocoding would be great.

Here's a Package.swift for flutter_geoconfig's iOS interface

Pitch

These changes will improve the developer experience and make the package future-proof when CocoaPods gets deprecated. Using SPM improves build times, so it will be beneficial for all Flutter projects to use SPM instead of CocoaPods, as Flutter suggests.