fix(nestsClient): bug + perf fixes from Nests implementation review

- send() now nulls currentGroup and returns false on uni-stream write
  failure (was: silently returned true while reusing the dead stream)
- Subscribe bidi gets a single long-running collector that closes the
  frames channel on peer FIN / transport tear-down (was: consumer
  could hang forever on a black-holed UDP path with no Announce(Ended))
- AudioException.Kind gains EncoderError; mic-side encode failures no
  longer mis-route through DecoderError handlers
- MoqCodec.decode bounds the payload-length varint before .toInt() so
  a peer-driven absurd length can't wedge the parser forever
- Publish hot-path framing collapses to a single ByteArray allocation
  (was: Varint.encode + plus operator, two allocs per Opus frame at
  50 fps)
- Drops the now-unused readSubscribeResponseFromBidi /
  readSizePrefixedFromBidiInto / EarlyExit helpers

Adds a regression test that asserts the frames flow completes when
the peer FINs the subscribe bidi.

213 tests pass, 0 failures.

nestsClient/src/androidMain/kotlin/com/vitorpamplona/nestsclient/audio/MediaCodecOpusEncoder.kt

@@ -66,7 +66,7 @@ class MediaCodecOpusEncoder(
         val inputBuffer =
             codec.getInputBuffer(inputIndex)
                 ?: throw AudioException(
-                    AudioException.Kind.DecoderError,
+                    AudioException.Kind.EncoderError,
                     "MediaCodec returned null input buffer at index $inputIndex",
                 )
         inputBuffer.clear()