Bump to 6.0.0: iOS 15.0 / macOS 12.0 minimums, CPython 3.12.15/3.13.16/3.14.8

[FeodorFitsner]

Fixes #254. Part of flet-dev/flet#6940.

Why

Xcode 27 rejects deployment targets below iOS 15.0 / macOS 12.0, and Flet 1.1.0 already moved its build template and client to those minimums (flet-dev/flet#6914). serious_python still declared iOS 13.0 / macOS 11.0, generated framework plists with MinimumOSVersion 13.0, and resolved iOS wheels for ios-13.0. The bundled runtime came from a python-build release built for the same old minimums.

Changes (6.0.0, a major bump because the minimum OS goes up)

• python-build re-pin: release 20261016 (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) brings CPython 3.12.15 / 3.13.16 / 3.14.8 and dart_bridge 1.11.0 (Release 1.11.0: raise Apple minimums to iOS 15.0 / macOS 12.0 dart-bridge#23). It's built for iOS 15.0 / macOS 12.0; the release's 3.12.15 Apple artifacts show minos 15.0 / 12.0 on every binary. lib/src/python_versions.dart and the four python_versions.properties were regenerated with gen_version_tables --release-date 20261016, and a second run produces no diff.
• serious_python_darwin:
  • podspec: s.ios.deployment_target = '15.0', s.osx.deployment_target = '12.0'.
  • Package.swift: [.iOS("15.0"), .macOS("12.0")].
  • xcframework_utils.sh: plists generated for native modules in site-packages say MinimumOSVersion 15.0.
• bin/package_command.dart: the iOS wheel platform tags are ios-15.0-*. sitecustomize reads the iOS release from the tag. packaging's ios_platforms() accepts every tag from 12.0 up to the target, so existing ios_13_0 wheels (e.g. on pypi.flet.dev) still resolve.
• Examples (bridge, run, flask):
  • iOS 15.0 / macOS 12.0 deployment targets and Podfile platforms.
  • Updated PODFILE CHECKSUMs in the Podfile.locks.
  • Dropped the jni: 1.0.0 override (see below).
• README.md: the minimum iOS/macOS sections now say 15.0 / 12.0, the CPython column shows the new patches, and the stale Pyodide column is fixed (→ 0.27.8 / 0.29.5 / 314.0.7).
• Version 6.0.0 in all 8 places, plus CHANGELOG entries in every package.

CI fix that isn't part of the release itself: jni override

The examples' dependency_overrides: jni: 1.0.0 worked around dart-lang/native#3498, an aarch64 Linux build failure that jni 1.0.3 fixed. jni_flutter 1.0.4+1, published 2026-10-06, has generated bindings that assert jni ^1.1.0. The override therefore broke every example build on every platform, main included, with "The generated bindings expect package:jni ^1.1.0, but 1.0.x was imported". This PR drops the override and moves the run/flask lockfiles to jni 1.1.0 / jni_flutter 1.0.4+1, the same fix as flet-dev/flet#6920.

Testing

• CI: every Android, Linux, Windows and web job passes. Each macOS and iOS combination (3.12 / 3.13 / 3.14 × CocoaPods / SwiftPM) passed in at least one of the two runs, push and pull_request. The red jobs are flakes:
  • macOS CocoaPods 3.12: pod install couldn't resolve cdn.cocoapods.org. It passed in the other run.
  • iOS CocoaPods 3.13 and 3.14: each hung after "Xcode build done" until the 25-minute timeout in one run and passed in the other. Recent main runs show the same iOS CocoaPods timeouts (e.g. runs 36267841941, 36073319160).
• Local, macOS: bridge_example packaged for 3.14, and interactivity_test passes. The app bundles CPython 3.14.8, Python.framework and dart_bridge are minos 12.0, and LSMinimumSystemVersion is 12.0.