atrac3: add boundary transient thresholding to prune low-value gain transitionsnew_psy_cont

Problem
Gain curve generation emitted many +/-1 level transitions that do not correspond
to strong local transients. These points consume gain-info bits and can create
low-level modulation artifacts without improving transient handling.

Solution
Introduce explicit transient evidence gating at transition boundaries in
CalcCurve(), and wire it to the existing dynamic min-score path.

What changed
- Added BoundaryTransientScore(env, loc, win):
  - computes local ratio around each subframe boundary
  - R = max(max_right/max_left, max_left/max_right)
  - short symmetric window (win=3 subframes)
- Re-enabled minScore usage in CalcCurve() (previously ignored).
- For each level transition candidate at loc=sf+1:
  - keep unconditionally if loc==targetSf (tail neutral anchor)
  - keep unconditionally if |deltaLevel| >= 2 (strong step)
  - otherwise keep only if BoundaryTransientScore(loc) >= minScore
- Added YAML telemetry:
  - transient_min_score
  - transient_window
  - transition_pruned {loc, delta, score}

Why this is safe
- Strong transitions are preserved.
- Rightmost transition is preserved to keep proper return-to-neutral anchoring.
- Only low-confidence small toggles are removed.

Measured impact (current branch comparison)
Baseline: ea4d33b38 (before this change)
Tracks: show_me_your_spine.wav, 13.wav

Gain-info bits / points:
- spine: 191,697 -> 150,297 bits  (delta -41,400; -21.6%)
         15,593 -> 10,993 points (delta -4,600)
- 13.wav: 1,299,035 -> 979,931 bits  (delta -319,104; -24.6%)
          97,035 -> 61,579 points   (delta -35,456)

Subjective note
User listening reports improved sound and fixes for some low-level artifacts.

0 files changed, 0 insertions, 0 deletions