Based on PR #2427 by @oxngon (core feature extracted, reformatting
and unrelated changes dropped).
Discord's TYPING_START gateway event is unreliable for bot DMs. This
adds a background typing loop that hits POST /channels/{id}/typing
every 8 seconds (indicator lasts ~10s) until the response is sent.
- send_typing() starts a per-channel background loop (idempotent)
- stop_typing() cancels it (called after _run_agent returns)
- Base adapter gets stop_typing() as a no-op default
- Per-channel tracking via _typing_tasks dict prevents duplicates
ab3cbfc99d