runtime: optimize MDEC FMV hot paths

Reconstruct the shareable pieces from PR #58 onto current master: add contiguous MDEC DMA input bursts, reduce per-pixel/per-byte MDEC output overhead, add sparse IDCT fast paths, and keep the MDEC activity stamp sane across rematches.

Also quiet the heavy debug trace recorders while MDEC video is active so debug builds can query state without starving FMV playback.

Regression testing was done with non-debug OpenGL builds across multiple FMV-heavy titles. Debug-tool FMV playback was also exercised with the quiet gate enabled.

Co-authored-by: Alex Vanderveen <alex@technicallycomputers.ca>

Co-authored-by: Cursor <cursoragent@cursor.com>

runtime/src/main.cpp

@@ -2609,6 +2609,7 @@ static void load_transition_note(int read_active, int load_active,
 /* Called from gpu_vblank_tick() at each simulated vblank. */
 static void sdl_vblank_present(void) {
 #ifndef PSX_NO_DEBUG_TOOLS
+    debug_server_set_fmv_quiet(mdec_recently_active(2));
     /* Debug server: pause gate, poll commands, record frame, check watchpoints. */
     debug_server_wait_if_paused();
     debug_server_poll();