feat(firebase): tvOS support for cloud_functions

[TheNoumanDev]

What does this PR do?

Adds federated cloud_functions_tvos — Firebase Cloud Functions (callable + streaming) for Apple TV, built on the Firebase Apple SDK. Re-exports the cloud_functions Dart API and ships the native tvOS pluginClass; depends on firebase_core_tvos. Full API, no feature disables.

Package(s) touched: cloud_functions_tvos (new)

How was it tested?

FirebaseFunctions.instance.httpsCallable(...).call() reaches the Cloud Functions backend (GTMSessionFetcher → us-central1-<project>.cloudfunctions.net) and returns the server's response. Platform.operatingSystem == "tvos" / Platform.isIOS == true.

• Ran the package's example/ app
• Verified on tvOS simulator (26.2) — callable round-trip to a live project
• Verified on a physical Apple TV 4K (tvOS 26.6, AOT) — same round-trip against a live project
• dart analyze is clean for the package

Versioning & changelog

• version: set to 0.0.1 (new package)
• Matching ## 0.0.1 entry at the top of CHANGELOG.md
• No behaviour change (new package)
• Semver 0.x: initial 0.0.1

Checklist

• Only cloud_functions_tvos files are touched
• No secrets, absolute local paths, or TODO/debug left
• README.md documents tvOS behaviour (full API; version-alignment note)
• Sibling-package constraint noted below

Notes for reviewers

• Version alignment (all Firebase _tvos leaf packages): the native Pigeon matches the firebase_core 4.11.x / firebase_core_platform_interface 7.1.0 train. Mixing firebase_core_tvos with a different firebase_core whose FirebaseOptions list differs can crash in CoreFirebaseOptions.fromList at launch (Dart options: init).

related issue: #13