Improve websocket reliability per Mist best practices (#26)

* Improve websocket reliability per Mist best practices

* Address PR feedback for websocket reliability changes

* Tune websocket logging and metrics thread safety

* fix(websockets): address review findings on reliability rework

- derive ping_timeout as min(45, ping_interval - 1) when not supplied, so
  existing callers passing only ping_interval keep working
- drain the callback queue on shutdown instead of dropping pending
  messages; the None sentinel now marks end-of-stream
- report subscription watchdog timeouts and subscribe_failed events
  through on_error so callers without auto_reconnect get a signal
- don't resurrect the callback worker after disconnect (stop flag is now
  only cleared by connect())
- cite the Mist rate-limits doc for the channel-count constants
- document the new reliability kwargs in all channel class docstrings
- add tests: ping derivation, worker drain, worker stop guard, watchdog
  expiry/cancel, subscribe_failed error reporting

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* docs(websockets): clarify ping_timeout derivation and queue_maxsize scope

- note that ping_timeout falls back to 45 when ping_interval=0 (pings
  disabled, value unused) in the constants comment, README, and all
  channel class docstrings
- document that queue_maxsize bounds both the receive() and callback
  queues in the channel class docstrings

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(websockets): reset reconnect state after subscriptions

* docs(changelog): add 0.63.3 websocket reliability notes

* fix: update version to 0.63.3 in pyproject.toml

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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>