v1.5.1 - Reloads during shutdown can no longer reconnect the light

Fluval BLE v1.5.1

v1.5.1 closes two gaps in the automatic Bluetooth release added in v1.5.0, so a
Home Assistant restart can never leave the Fluval light on a stuck connection.

Fixed

• A reload during shutdown can no longer reconnect the light. Once Home
  Assistant has started shutting down, the integration now refuses to set up
  again (including reloads and the delayed re-setup that fluvalble.release_link
  schedules). Previously a reload at exactly the wrong moment could open a fresh
  connection after the release had already run, and nothing would close it.
  A single process-wide "shutting down" marker, set at the very start of
  shutdown and never removed, now guards every setup and every delayed re-setup.

• Pressing "Return to schedule" during shutdown is no longer counted as a
  failure. The press is simply ignored, so it cannot raise a "schedule
  problem" repair that has nothing to do with the light.

Notes

No settings, entities or actions changed. fluvalble.release_link works as
before.