Bundle Python runtime built for iOS 15 / macOS 12; CPython 3.12.15/3.13.16/3.14.8

[FeodorFitsner]

Fixes #6940. Targets flet-1.1.0.

Why

#6914 moved the build template and the client to macOS 12.0 / iOS 15.0 for Xcode 27. The binaries flet build bundles still declared older minimums:

• Python.framework and the per-module Python frameworks: iOS 13.0 / macOS 11.0.
• dart_bridge: iOS 13.0 / macOS 10.15.
• serious_python podspec / SwiftPM: iOS 13.0 / macOS 11.0.

Those are now rebuilt for iOS 15.0 / macOS 12.0, and CPython moves to the latest patches:

• Release 1.11.0: raise Apple minimums to iOS 15.0 / macOS 12.0 dart-bridge#23: dart_bridge 1.11.0
• Bump Pythons to 3.12.15/3.13.16/3.14.8; iOS 15.0 / macOS 12.0 minimums; dart_bridge 1.11.0 python-build#46: python-build 20261016, with CPython 3.12.15 / 3.13.16 / 3.14.8. Pyodide is unchanged at 0.27.8 / 0.29.5 / 314.0.7.
• Bump to 6.0.0: iOS 15.0 / macOS 12.0 minimums, CPython 3.12.15/3.13.16/3.14.8 serious-python#256: serious_python 6.0.0, published on pub.dev

Changes

• flet_cli/utils/python_versions.py: PYTHON_BUILD_RELEASE_DATE 20260921 → 20261016, the same release serious_python 6.0.0 pins.
• Build template pubspec.yaml: serious_python: 5.0.0 → 6.0.0.
• CHANGELOG.md (1.1.0 → Improvements): added an entry for the update.
• minimum-macos-12-ios-15 breaking-change guide: notes that the bundled Python runtime, its native modules and dart_bridge use the same minimums, and links chore: Release serious_python and python_build with minimum iOS 15.0 #6940.
• flet_web/patch_index.py: fixed a stale Pyodide version comment.

Testing

• uv run pytest packages/flet-cli/tests/test_python_versions.py: 10 passed.
• I built a hello app that prints platform.python_version() from this branch with an empty cache (FLET_CACHE_DIR pointing at a new directory). Both builds resolved manifest-20261016.json and v3.14.8-20261016.
  • flet build macos: the app bundles CPython 3.14.8. Python.framework and dart_bridge are minos 12.0, and so are 98 of the 99 native modules. LSMinimumSystemVersion is 12.0.
  • flet build ios-simulator: Python.framework (3.14.8), dart_bridge and the app binary are minos 15.0. 120 of the 121 module frameworks are minos 15.0, and all 61 framework plists say MinimumOSVersion 15.0. The app's MinimumOSVersion is 15.0.
  • The only module below the floor is msgpack._cmsgpack, which comes from its PyPI wheel on macOS (10.15/11.0) and the pypi.flet.dev mobile-forge wheel on iOS (13.0/14.0). A lower minimum loads fine on a higher OS. Rebuilding the mobile-forge wheels for iOS 15 is a separate follow-up.

Summary by Sourcery

Align bundled Python and bridge dependencies with the iOS 15 and macOS 12 platform requirements while updating supported CPython patch releases.

Enhancements:

• Update the bundled Python runtime and native components to CPython 3.12.15, 3.13.16, and 3.14.8 with iOS 15 and macOS 12 deployment targets.
• Align the build template with serious_python 6.0.0 and dart_bridge 1.11.0.

Documentation:

• Document the updated minimum platform requirements for bundled Python components and dart_bridge.

Chores:

• Correct the documented supported Pyodide versions.

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