[kattni]

Release Python's GIL around UIApplicationMain, restoring the thread state on return or an Objective-C exception. Advertise sys._ios_app_main_releases_gil = True before importing app code so Rubicon can safely disable nesting. Refs beeware/rubicon-objc#846.

The complete fix requires this PR and beeware/rubicon-objc#847. Either component can be upgraded independently; only updating both disables nesting. No Toga or application code change is needed, but generated native launchers must be updated and rebuilt.

All four old/new Rubicon and launcher combinations passed the included simulator checks for nesting and prompt worker callbacks, as did a smoke test with unmodified Toga 0.5.7. Pre-commit passes; physical iPad trackpad validation remains outstanding.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by: OpenAI Codex