Fix faint slide starting partway down (#671)

The faint slide was shortened from 30 to Timing.FAINT_SLIDE (14) frames
in the timing-parity pass, but fxFaintOffset still computed the offset
with a stale (30 - frames) * 2.  With frames starting at 14 the sprite
teleported 32px down on the first frame and only slid the remaining
28px, cutting the animation short.

SlideDownFaintedMonPic drops the pic one 8px row per 2-frame step, so
the offset advances Timing.FAINT_SLIDE_STEP (4px) per frame at 1x and
covers the full 56px PIC_HEIGHT over the 14-frame budget.

src/core/Timing.lua

@@ -129,6 +129,7 @@ Timing.NO_MOVES_LEFT      = 60 -- core.asm:2753-2754
 Timing.TRAINER_VICTORY    = 40 -- core.asm:940-941
 Timing.PLAYER_BLACKOUT    = 40 -- core.asm:1143-1144
 Timing.FAINT_SLIDE_ROW    = 2  -- core.asm:1216-1217, per row
+Timing.FAINT_SLIDE_STEP   = 8 / Timing.FAINT_SLIDE_ROW -- 4px per frame at 1x
 Timing.TRAINER_SLIDE_COL  = 2  -- core.asm:1267-1268, per column
 
 -- HP bar (engine/gfx/hp_bar.asm) ---------------------------------------------