feat: Add analog and ping_pong delay subtypes under FXType.DELAY
- Refactor _apply_delay into subtype dispatcher (digital/analog/ping_pong/tape)
- Add _apply_analog_delay: BBD-style with one-pole LPF on feedback path
and subtle saturation (tanh) for warm, darker repeats. tone param
controls feedback brightness (0.0=dark, 1.0=bright).
- Wire existing _apply_ping_pong_delay and _apply_tape_echo as subtypes
- All existing delay tests (TestDelay, TestPingPongDelay) pass unchanged
- Add TestAnalogDelay: output range, dry passthrough, feedback tail decay,
tone spectral effect, state initialization, bypass
- Add TestDelaySubtypePingPong: output finite, dry path, state accumulation,
ping alternation, zero mix passthrough, bypass
Unblocks child task t_14bae7ea (FXBlock subtype field + pipeline dispatch)
shawn
adb35a730b