libfreemkv: phase-aware FMTS decode + two-operation KeyFetch/KeySource seam

FMTS (AACS 2.1) now decodes per (LBA, phase): Phase enum + AacsKeyMap::
from_ranges_phased, decrypt only the variant's parity half. resolve_fmts_key_map
does a 2-phase index-1 anchor then per-index phase probe, and sizes the forensic
set to whatever the source returns (no hardcoded 32). KeyFetch is now two explicit
operations (unit_keys / fmts_indexes) and KeySource splits get_uk into
get_unit_keys + get_fmts_indexes. BYPASS_FMTS_KEY gate removed (first-class format).

Teed up for 1.4.5. Local WIP baseline.

src/aacs/segment.rs

@@ -41,21 +41,6 @@ pub const SEGMENT_RECORD_LEN: usize = 16;
 /// Bytes per BDAV source packet (188-byte TS + 4-byte arrival-time header).
 pub const SOURCE_PACKET_LEN: u64 = 192;
 
-/// Whether a 2.1 (FMTS) disc may rip WITHOUT the forensic index keys.
-///
-/// `true` (today): the forensic segments are skipped as expected loss
-/// and the bulk of the title decodes with the unit key, so a 2.1 disc rips
-/// mostly-complete. A unit key (VUK) is still required, exactly as for any AACS
-/// disc. `false`: the absence of a segment-key source is a hard, UPFRONT failure
-/// ([`Error::FmtsKeyMissing`]) — the same policy as a missing unit key, so a
-/// forensic-holed rip is refused rather than produced. No segment-key source
-/// exists yet, so `true` is the only value under which a 2.1 disc rips at all;
-/// flip to `false` once segment keys can be sourced and a partial rip should be
-/// refused. Hardcoded on purpose — not a user setting.
-///
-/// [`Error::FmtsKeyMissing`]: crate::error::Error::FmtsKeyMissing
-pub const BYPASS_FMTS_KEY: bool = false;
-
 /// One forensic segment: the inclusive source-packet range it occupies in the
 /// FMTS clip.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]