Correct six stale comments and doc claims

All six describe code that does something different from what they say, which
is the class of defect that gets a maintainer to write a bug on purpose.

docs/clpi.md presented the CLPI stream-PID entry as byte-aligned 2/2/2/4/4-byte
fields with a 32-bit fine-entry count. It is one 80-bit packed block —
reserved(10) + EP_stream_type(4) + num_EP_coarse(16) + num_EP_fine(18) +
EP_map_start_address(32) — and num_EP_fine is 18 bits. Anyone parsing to the
doc's offsets would read garbage. Replaced with the real bit layout.

docs/udf.md said read_directory()'s recursion cap is 3; MAX_DIR_DEPTH is 8.

TROUBLESHOOTING.md called Pass 1 `recovery::copy`. The engine's `sweep` is
documented as "Pass 1 of a multipass rip"; `copy` is the dispatch verb that
chooses between sweep and patch. This inconsistency was mine, introduced in the
1.6.0 doc rewrite. docs/drive-access.md already said `sweep` and was right — a
round-2 finding claimed the opposite on the grounds that `recovery::sweep`
appears nowhere else in this crate, which it cannot, being in another crate.

io/pipeline.rs cited `disc::patch` as WRITE_THROUGH_DEPTH's caller; that moved
to freemkv-engine in 1.6.0 and no `patch` exists here.

truehd.rs's doc on mlp_major_sync_crc_ok said the trailer is compared
big-endian while the body compares u16::from_le_bytes — and a big-endian
compare was the bug the function was fixed for, so the comment described the
defect rather than the code.

sector/decrypting.rs claimed the decorator owns "the only mutable state (its
call-count cap and spent flag)". DecryptingSectorSource has no such fields and
no KeyFetch field at all in this revision.

src/mux/codec/truehd.rs

@@ -255,7 +255,8 @@ fn mlp_major_sync_header_size(ms: &[u8]) -> Option<usize> {
 /// 0x002D). The stored trailer is the last 2 header bytes; because
 /// MLP's checksum is byte-reversed relative to a standard CRC, a standard CRC of
 /// the header body XOR the little-endian word before the trailer must equal the
-/// trailer read big-endian.
+/// trailer read LITTLE-endian. (Comparing it big-endian was the bug this function
+/// was fixed for; the body and the inline note below are authoritative.)
 fn mlp_major_sync_crc_ok(ms: &[u8], mshdr: usize) -> bool {
     if mshdr < 4 || ms.len() < mshdr {
         return false;