[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

[freakboy3742]

I've removed the test case (since it wasn't being actively used); I've also been able to remove the sys annotation code, as my testing suggests that as long as we make the next Rubicon release 0.6.0, we can gracefully introduce the new lifecycle handling.