GPU threads: block instead of spin, and stay on the GPU's NUMA node

- set_gpu_blocking_sync(): every device is put in
  cudaDeviceScheduleBlockingSync before its context exists, so a host thread
  waiting on the GPU sleeps instead of spinning on a core. On a 16M rotation
  run a fifth of all CPU time was that spinning; wall time unchanged within
  noise. Called first thing in rugnux.
- enable_gpu_numa_binding(): from then on pin_gpu() (and the new
  pin_gpu(dev), used by the first-pass spot workers that take a card by
  index) also keeps the thread on the CPUs of the NUMA node the card hangs
  off. The node and its CPUs come from /sys (no libnuma), intersected with
  the process's own mask; Linux only, and nothing happens on a machine with a
  single node. rugnux turns it on; the broker does not.
- A thread inherits its creator's affinity, so the shared ParallelFor pool
  would run every later pass on one socket if a pinned worker created it:
  its threads now reset to the mask the process started with
  (common/ThreadAffinity).

Byte-identical output. The NUMA part is a no-op on the single-node test box
and still has to be measured on a two-socket machine.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D1G8gJVAy6gp1K5Dz3NE5C

common/CUDAWrapper.cpp

@@ -38,6 +38,12 @@ void set_gpu(int32_t dev_id) {}
 
 void pin_gpu() {}
 
+void pin_gpu(int32_t dev_id) {}
+
+void enable_gpu_numa_binding() {}
+
+void set_gpu_blocking_sync() {}
+
 void cuda_clear_error() {}
 
 #endif