Share finite SyncWait budget across event and feedback waits (#274)

Use only the remaining finite timeout after the fast-event wait instead of
starting a second full wait for feedback. Preserve polling, CPU completion
ordering and the existing infinite-wait stage caps.

Add deterministic regressions against the production wait function across
all three fast-wake sites and the four fast-wake/wait-ledger combinations.

Co-authored-by: smartLanny <51014844+smartLanny@users.noreply.github.com>

docs/reference/nvn-objects.md

@@ -185,6 +185,8 @@ Games read this count as a position in their own command memory and size their h
 - **Note:** the commit feedback handler's other blocks (diagnostics such as `DM_NVN_FUSE_CHECK`) still run when the handler does, after a fast-woken wait has returned.
 - **Resolved in review of #158:** claiming a record is not completion. The original early path skipped records a handler or another waiter owned and advanced `g_done` before their writes finished; a delayed callback also retained a recyclable slot pointer. `post_claim` now holds `g_post_mu` through `post_run`, and both contenders call `post_complete` with their fence to apply earlier records in order. A slot is reused under that lock only after its writes finish; an old fence cannot claim its new generation. `g_done` and `g_fence` are atomic.
 - **Check:** `make -C dm/gfx/tests GAME=010015100B514000 check_t_perf_order` covers a paused completion owner, a competing waiter, recycled-slot generations, event order and exactly-once writes, with direct/deferred encoding and fast wake disabled. `t_perf_order --cpu` and `perf-order-tsan` run the completion cases without a GPU in CI. The original harness reproduced premature completion; the corrected CPU cases pass ThreadSanitizer. Current gameplay coverage and timing limits are recorded in [BotW](../../dm/games/01007EF00011E000/README.md#final-synchronization-and-pass-validation-2026-10-26-current) and [Metroid Dread](../../dm/games/010093801237C000/README.md#final-gameplay-validation-2026-10-26-current); [13 Sentinels](../../dm/games/01003FC01670C000/README.md#rendering) has additional menu/report traffic coverage.
+- **Finite timeout budget:** when the event wait times out, the feedback wait uses only the remaining requested time. Previously an expired 20 ms event wait could be followed by another full 20 ms feedback wait. Elapsed time is taken from the monotonic wait clock independently of wait diagnostics. Zero/sub-millisecond polls, successful CPU completion, and the existing per-stage one-hour cap for `UINT64_MAX` are unchanged. This bounds the time assigned to the two waits, not scheduling delays or the CPU completion lock.
+- **Budget regression:** the `--cpu` path also uses a synthetic event, clock and condition-wait deadline to exercise the actual `mtl_wait_at` function without a Metal device. Run with `DM_NVN_FAST_WAKE=0/1` and `DM_NVN_WAITS=0/1`; no gameplay or FPS improvement is inferred from these timeout cases.
 - **Found on:** [The Legend of Zelda: Breath of the Wild](../../dm/games/01007EF00011E000/README.md): it reads 5 timestamp reports a frame right after the wait (its interval controller and dynamic resolution), which is why the waiter makes them itself. Wake after the GPU end 0.29 → 0.08 ms on an M2 Max, 0.147 ms on an iPhone 17 Pro Max.
 
 ### `nvnQueueFinish` waits for the GPU, not the display