Check a busy slot fence before waiting for its thread-pool callback.
This lets the caller complete finished GPU work inline and avoids a
scheduler delay before the allocator and command list can be reused.
Signal a per-slot event after callbacks finish and the command slot has
returned to the free state. This removes the one millisecond polling delay
when candidate state becomes visible just before its slot is reusable.
Replace the rotating D3D12 copy queues with two framebuffer-bound
recording slots on one physical COPY queue. Keep allocator, command
list, query range, callback state, and fence target independent per
slot.
Submit source waits, execution, and signaling on the shared timeline.
Track framebuffer ownership through completion and serialize LGMP
publication around the last successfully published frame.
Use calibrated copy-queue timestamps to separate source and effect
waits from the actual framebuffer copy.
Exclude producer readiness waits from client import timing so the
same interval is not counted in both Copy and Import.
The callback runs in a random thread, we can't call directx methods
safely from it, so move reset so it's called automatically when a free
copy list is obtained.
