Samplemento — Attack no longer shortens sample

Built from the confirmed-good STARTEND_SAFE version.

Cause:
The envelope timing path multiplied Attack by 2 and subtracted it from the
available sample playback duration. Therefore larger Attack values caused the
sample's end envelope to be scheduled earlier.

Fix:
That compensation is now zero. Attack controls only the fade-in timing and no
longer removes time from the sample playback.

Unchanged:
- 1200 ms max Attack
- 1% minimum/startup Attack initialization
- retrigger declick
- 25 ms end fade
- conservative Start/End fix
- separate Reverse function
