fix(dab): stop ETI reader and release refcount on shared-mode teardown

Two fixes from code review:

1. Stop _eti_reader in Dablin.stop() (shared mode) — previously the cursor
   remained registered on SharedDabDecoder._eti_buffer after disconnect,
   forcing the buffer to retain data from the disconnected client's position
   until GC. With rapid connect/disconnect cycles this caused transient buffer
   bloat.

2. Release shared decoder refcount in _getDemodulator fallback path — if
   acquire() succeeded but Dablin.__init__ subsequently raised, _dabKey was
   cleared without calling release(), leaking one refcount and preventing the
   shared decoder from ever stopping.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

csdr/chain/dablin.py

@@ -155,6 +155,9 @@ class Dablin(BaseDemodulatorChain, FixedIfSampleRateChain, FixedAudioRateChain,
             self.processor.stop()
         else:
             self._meta_forwarder.stop()
+            if self._eti_reader is not None:
+                self._eti_reader.stop()
+                self._eti_reader = None
 
     def setMetaWriter(self, writer: Writer) -> None:
         if self._shared_decoder is None:

owrx/dsp.py

@@ -596,7 +596,9 @@ class DspManager(SdrSourceEventClient, ClientDemodulatorSecondaryDspEventClient)
                 return Dablin(shared_decoder=shared)
             except Exception:
                 logger.exception("Shared DAB decoder failed, falling back to standalone")
-                self._dabKey = None
+                if self._dabKey is not None:
+                    DabDecoderManager.getShared().release(*self._dabKey)
+                    self._dabKey = None
                 return Dablin()
         elif demod == "empty":
             from csdr.chain.analog import Empty