Rebuild object lifetime and run native events through a mailbox per loop, add free-threaded and 3.15 wheels

[MarshalX]

Rebuilds wrapper lifetime on one ownership rule (LIFETIME in cpp/NATIVE.md):

• Unreferenced connections, channels and live tracks stay alive while they have handlers or pending work, until they close or their loop closes
• Events and native call results go through a mailbox per event loop, so native threads never run Python
• One wrapper per native object; wrappers take no attributes
• Free-threaded Python: cp314t and cp315t wheels, plus CPython 3.15
• Remote tracks fire ended on close; a failed RTCIceTransport survives for an ICE restart
• Tests wait on conditions, not sleeps

[read-the-docs-community]

Documentation build overview

📚 wrtc | 🛠️ Build #35076065 | 📁 Comparing 07bb6fc against latest (99ad508)

  🔍 Preview build  

16 files changed · + 1 added · ± 15 modified

+ Added

• search/index.html

± Modified

• index.html
• api/index.html
• change_log/index.html
• api/base/index.html
• api/events/index.html
• api/streams/index.html
• guides/connections/index.html
• guides/data-channels/index.html
• guides/events/index.html
• guides/media/index.html
• and 5 more...