Handle WebSocket disconnects cleanly in streamer _reader

[ccjoeg]

Summary

• Adds StreamerDisconnect exception (with code and reason attributes) to tastytrade.utils
• Catches WebSocketDisconnect and WebSocketNetworkError in both DXLinkStreamer._reader and AlertStreamer._reader, re-raising as StreamerDisconnect
• Unwraps StreamerDisconnect from the ExceptionGroup in DXLinkStreamer.__asynccontextmanager__ so callers receive a plain exception
• Exports StreamerDisconnect from the package __init__.py

Motivation

When the DXFeed WebSocket drops — whether from a network error or a server-requested reconnect (close code 1012, SERVICE_RESTART) — the raw httpx_ws exceptions (WebSocketNetworkError, WebSocketDisconnect) propagate uncaught from _reader. This crashes the anyio TaskGroup and surfaces as an ExceptionGroup with a full traceback:

ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | httpx_ws._exceptions.WebSocketDisconnect: (<CloseReason.SERVICE_RESTART: 1012>, 'Reconnection is required')
    +------------------------------------

This makes it difficult for callers to:

1. Distinguish routine disconnects from actual errors
2. Implement appropriate retry strategies (e.g. immediate reconnect for code 1012 vs longer backoff for network failures)
3. Log cleanly without noisy tracebacks for expected events

Usage

After this change, callers can catch StreamerDisconnect and inspect e.code:

from tastytrade import DXLinkStreamer, StreamerDisconnect

while True:
    try:
        async with DXLinkStreamer(session) as streamer:
            # ... subscribe and listen ...
    except StreamerDisconnect as e:
        if e.code == 1012:
            await asyncio.sleep(5)   # server-requested, reconnect quickly
        else:
            await asyncio.sleep(30)  # network error, back off

Test plan

• Verify existing streamer tests still pass
• Verify StreamerDisconnect is raised (not ExceptionGroup) on WebSocket close
• Verify e.code is populated correctly for WebSocketDisconnect (e.g. 1012)
• Verify e.code is None and e.reason is "network error" for WebSocketNetworkError

🤖 Generated with Claude Code

[Graeme22]

Please use the pattern from the docs: https://tastyworks-api.readthedocs.io/en/latest/data-streamer.html#auto-retries