transcode: improve logging of packet transcode errors

transcode: improve logging of packet transcode errors

Improve visibility of decoding failures during transcoding by logging
the error code, a human-readable description, and the packet PTS when
the hardware decoder fails to process a packet.

Previously, these errors would silently trigger `tvh_stream_stop()` on
the affected stream, with minimal context about the underlying cause.
This made it difficult to diagnose issues such as hardware acceleration
glitches or codec-specific decode failures.

With this change, such errors are logged at warning level, and full
packet details are included if trace logging is enabled. This provides
valuable diagnostic information when investigating stream interruptions
or video dropout.

This commit does not alter transcoder behavior; errors are still
filtered or handled by other components as before. It simply makes
decoder error conditions more transparent for debugging purposes.