Performance diagnostics and small wins for title 1

- eden-cli: SDL called SDL_AppIterate back to back, keeping a host core at
  100% polling input; run the main callbacks at 240 Hz.
- EDEN_NX2_IDLE_SPIN_US: optional spin before an idle core blocks (measured:
  no gain on title 1, so off by default).
- EDEN_NX2_SVC_TRACE=<first>:<last>: trace SVCs (with thread ids) for a range
  of presents only.
- MME DMA reads flush GPU-written memory first (never triggered on title 1,
  kept for correctness); render-enable override histogram instead of the
  first-400 log.

Measured on title 1's title screen (RTX 4070 Laptop): GPU ~20% busy, the six
emulated cores ~0.9 host cores in total, Eden's GPU thread 45-70% busy and
largely waiting: on host fences for semaphore acquires (GPU accuracy High
delays every release to host completion), on ASTC upload Finish(), and in a
1 ms poll sleep. gpu_accuracy=Low: ~12.5 -> ~16 fps.

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