feat(v2): add websocket client with typed events, reconnect, and tests

[tomquist]

Summary

This PR adds HomeWizard v2 WebSocket support (/api/ws) with authentication, reconnect handling, typed events, docs, and tests.

Added

• New HomeWizardEnergyWebSocket client in homewizard_energy/v2/websocket.py
• HomeWizardEnergyV2.websocket() helper to create a websocket client
• Public exports:
  • HomeWizardEnergyWebSocket
  • WebSocketTopic
  • HomeWizardEnergyWebSocketEvent

WebSocket behavior

• Connects to wss://<host>/api/ws
• Handshake flow:
  • wait for authorization_requested
  • send authorization with token
  • require authorized
• Token is required (UnauthorizedError when missing)
• Keeps handshake serialized under lock and only exposes self._ws after auth completes
• Handles dropped connections with reconnect/backoff
  • exponential backoff with jitter
  • avoids reconnect loops for externally owned + closed sessions

API additions

• Raw API remains available:
  • send, receive, events, subscribe, unsubscribe, identify, request
• Typed API added:
  • receive_typed()
  • events_typed(reconnect=...)
  • WebSocketTopic enum for topic-safe subscribe/request calls
• Best-effort model decoding for known topics:
  • device -> Device
  • measurement -> Measurement
  • system -> System
  • batteries -> Batteries

Error handling / lifecycle

• Normalizes websocket receive/send failures to RequestError
• Handles websocket { "type": "error" } payloads as RequestError
• Guards against shared-session lifecycle issues and clarifies ownership in docs
• Serializes close/reconnect teardown with lock

Documentation

• Updated README.md websocket example to use typed API (WebSocketTopic, events_typed)

Tests

Added tests/v2/test_v2_websocket.py covering:

• token requirement and handshake
• invalid handshake
• helper payloads for subscribe/unsubscribe/identify/request
• websocket error payload handling
• invalid JSON shape handling
• reconnect on dropped socket
• reconnect after transient connect failure
• no reconnect when externally owned session is closed
• typed event decoding

Note that I wasn't able to test this change E2E because I don't own a HomeWizard device.

Validation

• pre-commit run --all-files ✅
• websocket/v2 targeted tests pass locally

Fixes #599