Real aligner alternatives: MFA / aeneas behind the Aligner seam

[thorwhalen]

Real aligner alternatives: MFA / aeneas behind the Aligner seam

WhisperXAligner (foley[align]) is the shipped real forced aligner; the Aligner protocol
seam is open. MFA (Montreal Forced Aligner) and aeneas were reserved because both carry
heavy/awkward install stories (conda for MFA; espeak/ffmpeg C deps for aeneas) ill-suited to a
plain pip extra.

Scope

• Add MFAAligner and/or AeneasAligner behind the existing Aligner protocol, lazy-imported,
  with importorskip-guarded round-trip tests (mirroring WhisperXAligner).
• Document the install path per aligner (conda / system deps) and how to inject it
  (weave(..., aligner=…) / foley.score(..., aligner=…)), plus a comparison note
  (accuracy vs footprint vs license) so users pick deliberately.
• Keep the deterministic FakeAligner as the default; no new hard dependency.

Acceptance

• A user with MFA (or aeneas) installed can inject it and get word timings; CI stays hermetic.