CSS DVD mux: per-title key via scan-key reuse + playback-order crack

A CSS DVD whose main title was mis-detected as unencrypted (the up-front
crack scanned the largest cell first and starved its budget in that cell's
clear prefix) muxed scrambled sectors as plaintext at exit 0. CSS leaves
the pack/PES header clear, so an un-descrambled sector muxes as a
structurally-valid but corrupt PES packet with zero loss reported.

decrypt_keys_for_title resolves a DVD title's CSS key two ways:
- Fast path: reuse the scan's cracked key when its crack_span covers this
  title's VTS (no re-read; on a live drive no second bus-auth).
- Crack: on a detection miss or a different VTS, crack from the title's OWN
  extents in a SINGLE scan in natural PLAYBACK ORDER (never largest-first).
  One scan = one CSS-locked early-bail, so a locked title is not re-hammered
  per cell against a live drive (hard rule #2); the 50k-sector budget is the
  same accepted bound the disc-wide scan uses. Cracked -> key; Unencrypted
  -> clear; ScrambledUncracked -> hard-fail.
ensure_title_decryptable hard-fails an uncrackable DVD title even when
detection missed, and passes a title that resolved its OWN valid key
regardless of the disc-wide css_error. descramble_region is unchanged from
v1.5.1 (validated-key seed).

Also rename the unlocker report's DVD entry CSS -> DVD. Bump 1.5.2.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "libfreemkv"
-version = "1.5.1"
+version = "1.5.2"
 edition = "2024"
 rust-version = "1.86"
 license = "MIT"