mmx6 framework: CD/DMA/MDEC + codegen fixes (Tomba builds+plays, MMX6 boots to intro)

Framework work on codex/mmx6-support that makes Tomba build and play
(title screen, 0 dispatch misses) and MMX6 boot through BIOS to its
intro. Touches recompiler codegen (code_generator, function_analysis)
and runtime CD-ROM/DMA/MDEC/GPU/SIO timing (cdrom, dma, mdec, gpu,
psx_cycles, traps, fntrace, debug_server) + headers + runtime.cmake.

Milestone snapshot for collapsing onto master. Build dir excluded.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

runtime/include/debug_server.h

@@ -166,6 +166,10 @@ void debug_server_check_watchpoints(void);
  * -1 if no override is active. Value is PS1 16-bit button mask. */
 int debug_server_get_input_override(void);
 
+/* TCP-controlled turbo mode. When enabled the frontend skips presentation and
+ * wall-clock pacing at vblank, matching the keyboard TAB turbo path. */
+int debug_server_turbo_enabled(void);
+
 /* ---- Send helpers (for extensions) ---- */
 
 /* Set the CPU state pointer for register queries. Call after CPU init. */