Connection-quality indicators for Calls SDK

Summary
Add a connection-quality signal to the Calls SDK so apps can warn users when their connection, or another participant’s, is getting worse during a call.

Current state
v4 has no connection events. v5’s onConnectionLost / onConnectionRestored only report the local connection dropping and reconnecting. There’s no quality level and nothing for remote participants.

Proposal

• A quality-level event (e.g. GOOD / FAIR / POOR) for the local user and for each remote participant

• Optional raw stats (packet loss, round-trip time, jitter, bitrate)

• Available on iOS and Android first, then the other platforms, and exposed in the UI Kit

Why
Users get no warning before a call degrades or drops, so a network problem looks like the app failing.