1.6.0: remove recovery strategy (moved to freemkv-engine) + trim dead surface

The sweep/patch recovery strategy, mapfile, retry-decision state machine,
section-recover, and damage classification move out of libfreemkv into the
new freemkv-engine crate. libfreemkv keeps the raw single-shot read and
SCSI-fact translation (SenseFamily stays in scsi).

- Delete disc/{sweep,patch,mapfile,read_error,section_recover}.rs, the
  Disc::copy/sweep/patch methods, the Copy/Sweep/Patch option+result types,
  classify_damage/DamageSeverity, progress_snapshot_from_mapfile, and the
  three recovery integration tests.
- Trim public surface the recovery deletion orphaned: delete the dead
  READ_PIPELINE_DEPTH const, the write-side SectorSink/FileSectorSink (no
  consumer), and the DriveSpeed enum (its one live use — set max drive
  speed — becomes Drive::SPEED_MAX_KBPS). Make mapfile_path_for,
  decrypt_sectors_mapped pub(crate); gate NoopEvents to test.
- Version 1.6.0.

src/disc/extract.rs

@@ -1,6 +1,7 @@
 //! `Disc::extract_tree` — decrypted file-tree extraction (`dir://`).
 //!
-//! Sibling of [`Disc::copy`](super::Disc::copy) (disc → ISO sector dump),
+//! Sibling of the disc→ISO sector dump (the sweep/patch recovery passes, which
+//! now live in the `freemkv-engine` crate),
 //! specialized to write **per file** rather than a whole image, applying
 //! decryption on the way out, and **without** any multipass / recovery
 //! orchestration. 1-shot, decrypt-only.