Revive CI

[ofalvai]

History and background context:

• Azure CI config is the original one. It also contains internal Microsoft tooling that is no longer relevant.
• GHA config was added in f149a12, but it wasn't a 1:1 migration
• The jobs ios-old-arch-test and android-new-arch-test are broken since Add Rn 0.82.1 support codemagic-ci-cd/react-native-code-push#33, which dropped RN old arch support.

Changes

• Delete Azure CI pipeline configs, but migrate the actual CI logic to GHA
• Set up a quick lint job that runs first and doesn't involve slow sample app builds, emulators/simulators.
• Make the Android and iOS test jobs actually work:
  • Android: this was already in a good shape. We use the de-facto https://github.com/ReactiveCircus/android-emulator-runner instead of the shell script tweaks in the old Azure config.
  • iOS: had to fix one known issue between RN 0.82 and Xcode 26.4+, and also revert one change that I'm 90% sure caused a real regression. It's the Codepush.m workaround introduced in this commit. Dispatching to another thread definitely broke the revert logic, it resulted in 6 broken iOS test scenarios. Meanwhile, I couldn't reproduce that race condition mentioned in the workaround, so I think we better revert that workaround, it at least fixed the revert logic. Even if that race condition is real, it might be already fixed upstream (we are testing with RN 0.82 at the moment, latest stable version is 0.86)
• Set up tool version pinning via Mise and mise.toml.
• Runners (runs-on): set up some org-wide hosted large runners. On the Linux side, these are needed because of nested virtualization, and the default macOS runners are too weak for our stuff.

Out of scope

• Optimize CI performance or reliability: later
• Revisit Node/JDK/etc tool version, do upgrades: later

[ofalvai]

TODO: upgrade