SpanMqttClient:
- snapshot_interval and set_snapshot_interval() now raise ValueError
  below 1.0s, removing the <=0 immediate-dispatch branch that could
  spawn unbounded per-message dispatch tasks on a busy broker.
- Connection-callback exceptions logged at WARNING (matches
  _dispatch_snapshot); the old exception() level implied a fatal
  error that the bridge handles cleanly.
- _wait_for_circuit_names uses time.monotonic() instead of the
  deprecated asyncio.get_event_loop().time() pattern.

AsyncMqttBridge:
- Build ssl.SSLContext from fetched PEM via cadata and pass it
  with tls_set_context() instead of writing the CA to a temp file.
  Eliminates the file cleanup lifecycle and its crash-time leak.
- _reconnect_loop catches all exceptions (not only OSError) so
  transport-specific failures like WebsocketConnectionError or
  ssl.SSLError no longer kill the background task silently.
- Abnormal disconnects (reason_code.is_failure) log at WARNING.

HomieDeviceConsumer:
- _build_circuit: explicit -0.0 suppression replaces the cryptic
  `-raw or 0.0` idiom.
- _derive_dsm_state: grid-exchanging check uses an epsilon
  (1.0 W) instead of != 0.0 float comparison, so DSM_OFF_GRID
  is reachable when lugs readings hover near zero.

- get_fqdn() returns str | None so callers can distinguish
  "no FQDN configured" (HTTP 404 or missing ebusTlsFqdn field)
  from an explicit empty string. Callers that treated "" as
  "not registered" must now check for None.
- SpanPanelAPIError: remove custom __str__ override that silently
  truncated args[1:]; the default Exception.__str__ is more useful.
- register_v2(): docstring warns that each call accumulates a new
  registered-client entry on the panel, so callers should persist
  and reuse the returned V2AuthResponse rather than re-registering
  on every restart.

NullLock monkey-patches a hardcoded list of paho-mqtt's internal
*_mutex attributes. A paho minor-version refactor that renames or
adds locks would silently break the override.

Add a bidirectional check at module import: every attribute we
list must exist on paho.Client, and no other *_mutex attribute
may be present. Raise RuntimeError on drift (not assert, so
python -O does not bypass it).

- Record 2.6.1 changes in CHANGELOG.
- Remove "MQTT and simulation transports" / "REST polling or MQTT
  push" wording from protocol.py and models.py module docstrings.
  The simulation and REST transports were removed in 2.0.0.

The 1.0s floor was based on a misread of the integration constraint:
the integration can be configured with scan interval 0 for real-time
updates, so the library must not reject it.

Restore the <=0 immediate-dispatch path and drop the ValueError
validation from both __init__ and set_snapshot_interval(). Tests
updated to cover real-time dispatch for interval=0 and interval<0.
CHANGELOG and README reverted.