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/inverter.py

@@ -284,6 +284,12 @@ class Inverter:
         # SMA-10. Writes to a hand-back driver that are on their way (see
         # Controller._write_unit), so the release can wait for them and be LAST.
         self.inflight: set = set()
+        # SMA-10 round 2. A failed hand-back: how many tries in a row failed
+        # (the log is written at the first and on recovery only), when the next
+        # try is due (monotonic s), and whether the one fallback 0 W was sent.
+        self.release_fails = 0
+        self.release_retry_at = 0.0
+        self.release_zero_sent = False
         self.last_write_ok = None
         # ⚠️ TWO TIMESTAMPS, NOT ONE FLAG. `last_write_ok` is the last write's
         # verdict and it flips on a single transient 400; liveness needs a RUN