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/disc/encrypt.rs

@@ -976,7 +976,7 @@ mod tests {
     /// A minimal in-test KeySource that yields no keys but a fixed cert list.
     struct CertSource(Vec<aacs::types::HostCert>);
     impl crate::KeySource for CertSource {
-        fn get_uk(
+        fn get_unit_keys(
             &self,
             _ctx: &dyn crate::keysource::ResolveCtx,
         ) -> Result<Vec<crate::aacs::types::UnitKey>> {