Interop between Flutter and Python using Dart NativeAPI and FFI

[FeodorFitsner]

Write Python native extension in C that uses Dart ports.

Examples:

• https://realpython.com/build-python-c-extension-module
• https://github.com/audiooffler/JucyFluttering/tree/master
• https://github.com/mraleph/go_dart_ffi_example/blob/master/godart.go
• https://codebrowser.dev/dart_sdk/dart_sdk/runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc.html

Passing *void:

• https://stackoverflow.com/a/20411505
• https://stackoverflow.com/questions/68485874/how-do-you-correctly-pass-a-pointer-between-calls-with-python-c-api

Discussions:

• How to use async callback between C++ and Dart with FFI? flutter/flutter#63255 (comment)
• [Dart FFI] How to pass a Struct via Dart_PostCObject_DL? dart-lang/sdk#47048
• https://stackoverflow.com/questions/65865190/flutter-dart-ffi-aplication-freezes-during-processing-external-library-metho