mux: FMTS reads only our-phase units (AacsKeyMap::read_plan)

An FMTS forensic segment interleaves our device group's variant with a
foreign group's at the aligned-unit level. The mux was decrypting only
our phase but leaving the alternate (foreign) units in the buffer as
ciphertext, trusting the demux to 'drop untouched ciphertext cleanly'.
It doesn't: random 0x47 bytes at the 192-byte stride hit tracked PIDs,
mis-parse, and trip the demux's concealed-gap keyframe-resync — which
drops GOOD frames of ours around every segment (349 resyncs / ~6391
packets on Stand by Me, visible as playback flaws).

The map already knows which unit each LBA is and, for a forensic
segment, which phase is ours. AacsKeyMap::read_plan turns that into the
title's read plan: every default/CPS unit, plus inside a segment ONLY
our-phase units. The alternate units are never fetched, decrypted, or
handed to the demux — the demux sees one gapless our-variant stream.

- read_plan is general (single-CPS, multi-CPS, FMTS): a map with no
  Even/Odd range returns the extents unchanged, so DVD/CSS, single-CPS
  UHD and multi-CPS Blu-ray read byte-for-byte as before.
- Wired into build_iso_pipeline (the file-backed highway that muxes
  resumed ISOs). Producer re-anchors unit_base per extent, so per-unit
  segment reads stay unit-aligned and decrypt correctly.
- Extent gains PartialEq/Eq for the read_plan tests.

Tests: read_plan non-forensic unchanged; forensic omits exactly the
alternate units, kept units match the decrypt gate unit-for-unit. All
2314 lib tests pass; precommit green on 1.86.

Pending: end-to-end ISO re-mux validation (concealed gaps 349 -> ~0).

src/mux/resolve.rs

@@ -1038,6 +1038,18 @@ pub fn build_iso_pipeline<S: SectorSource + Send + 'static>(
             )),
             _ => None,
         };
+    // The map IS the title's read plan: it says which CPS unit / forensic segment
+    // each LBA belongs to. Walk ONLY the units it marks as ours — every default /
+    // CPS unit, and inside an FMTS forensic segment only our-phase units. The
+    // alternate-phase units are a different device group's variant; a licensed
+    // player never reads them, and neither do we — they are never fetched,
+    // decrypted, or handed to the demux, so the demux sees one gapless our-variant
+    // stream (no ciphertext to trip a concealed-gap resync). A non-forensic map
+    // returns the extents unchanged, so the common disc reads exactly as before.
+    let extents = match &key_map {
+        Some(map) => map.read_plan(&extents, unit_align as u32),
+        None => extents,
+    };
     let mut decrypting =
         crate::sector::DecryptingSectorSource::new(Box::new(reader) as Box<dyn SectorSource>, keys);
     if let Some(map) = key_map {