SMA-10 round 2: a failed release sends 0 W once, retries at heartbeat pace

When release() fails (False, raises or hangs past RELEASE_BUDGET_S) the unit
gets one bounded write(0) through the new Driver.release_fallback() hook
(default write(0)), then nothing more, so the inverter's own fallback timer is
not reset. The release is retried once per heartbeat, not on every idle
write. One error line and one action-log event per failure streak, one line on
recovery. Dutch default "terug naar de eigen sturing". DECISIONS says what a
unit is left at.

test_messages.py: the RELEASE_BUDGET_S data entry is gone again (the line
that needed it is gone).

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

goodwe_controller/app/drivers.py

@@ -160,6 +160,14 @@ class Driver:
         never a release: that is `write(0)`."""
         return await self.write(0.0)
 
+    async def release_fallback(self) -> bool:
+        """SMA-10 round 2. What to send, ONCE, when `release()` has failed
+        (False, raised, or hung past the bound), so the unit does not carry its
+        last command while nothing else steers it. Default: `write(0)`. It is
+        not repeated: a repeat would keep resetting the inverter's own fallback
+        timer. A driver for which 0 W is not always a safe hold overrides this."""
+        return await self.write(0.0)
+
     async def probe(self) -> Probe:
         """A read-only look, usable without a Controller (panel, wizard)."""
         raise NotImplementedError