Stop the live rip path muxing Blu-ray 3D differently from the ISO path

Five defects, four of them the same shape: a local reimplementation of
logic the crate already had, which had drifted from it. Each is now fixed
by calling the canonical version rather than by patching the copy.

DiscStream::new — the live disc:// path — built every parser through the
plain codec lookup and never asked whether a video stream was an MVC
dependent view, though resolve::build_demux_state does. The same 3D disc
therefore muxed correctly from an ISO and incorrectly ripped live. The
open-coded loop is gone; both paths now call build_demux_state.

collect_psi_section reimplemented the continuity-counter gap test and
disagreed with process_packet in the same file: it tolerated neither a
duplicate packet nor an adaptation-field-only packet, which per ISO/IEC
13818-1 §2.4.3.3 does not increment the counter. A spec-legal PMT
continuation was read as desync and the title's stream list came back
empty. Both callers now share one `cc_is_gap`, and a duplicate packet's
payload is no longer appended twice — doing so would have corrupted the
section the check exists to protect.

The json:// sink called the channel-count and sample-rate accessors
unconditionally, and both fabricate a concrete value for Unknown, so it
reported a confident 5.1 at 48 kHz for audio whose format was unknown
while its own neighbouring string fields said "unknown". The keys are now
omitted, matching mkv.rs. This matters more than it did: a sample-rate
ladder fixed earlier in this audit means Unknown now reaches consumers
that used to receive a wrong-but-concrete value.

For an audio:// or sub:// sink the reference video track's output is
filtered out, so its first PTS was never recorded and every delay was
computed against zero — baking a wrong DELAY into the filename. The
reference is now recorded whenever a frame is on the reference track,
independent of whether that track has an output, so a normal title gets a
correct delay; where no reference is ever observed the tag is omitted
rather than guessed.

A third copy of the channel/sample-rate mapping exists in src/diag.rs and
was left alone as outside the confirmed set. It is the same drift shape
and is recorded for the next round.

src/mux/resolve.rs

@@ -720,7 +720,7 @@ pub fn output(
 /// table (keyed by PID), the PID-to-track index map, and an initial
 /// `TsDemuxer` / `PsDemuxer` (whichever the content format calls
 /// for).
-type DemuxState = (
+pub(crate) type DemuxState = (
     Vec<(u16, Box<dyn super::codec::CodecParser>)>,
     Vec<(u16, usize)>,
     Option<super::ts::TsDemuxer>,
@@ -729,7 +729,7 @@ type DemuxState = (
 
 /// Build the title's codec parser table + initial `TsDemuxer` /
 /// `PsDemuxer`. Used by both the ISO and M2TS pipeline builders.
-fn build_demux_state(title: &DiscTitle, format: ContentFormat) -> DemuxState {
+pub(crate) fn build_demux_state(title: &DiscTitle, format: ContentFormat) -> DemuxState {
     let mut pids = Vec::new();
     let mut parsers = Vec::new();
     let mut pid_to_track = Vec::new();