[kattni]

Make iOSLifecycle() automatically avoid nesting when the native launcher sets sys._ios_app_main_releases_gil to True. Older launchers retain nesting; explicit overrides remain available. Refs #846.

The complete fix requires this PR and beeware/briefcase-iOS-Xcode-template#91. Either component can be upgraded independently; only updating both disables nesting. Existing Toga and application code work unchanged. Generated native launchers must be updated and rebuilt.

All four old/new Rubicon and launcher combinations passed simulator checks for nesting and prompt worker callbacks, as did a smoke test with unmodified Toga 0.5.7. macOS Python 3.11–3.15, the full iOS suite, docs, pre-commit, and Towncrier checks pass. 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]

As noted on the template, I think this can be significantly simplified if we make the next release 0.6.0, and add a release note in the next Toga release.