setDriverCallbacks renamed to setLaunchCallbacks in upstream proton.

The simple 500μs interval check could only pass 2000 samples/sec
regardless of actual load. The token bucket (configurable via
PARCAGPU_RATE_LIMIT, default 100/sec) smooths bursts while
maintaining a predictable average rate.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add parcagpuActivityBatch() probe that fires with batches of up to 128
activity record pointers, enabling BPF consumers to read kernel timing
data directly from CUPTI buffers without per-record probe overhead.

Build/test changes:
- Link test binary against mock CUPTI/CUDA with --no-as-needed so
  Proton's dlopen(RTLD_NOLOAD) finds the mocks at runtime
- Fix make test to run the test binary directly with LD_LIBRARY_PATH
  (ctest had no tests registered)
- Add make bpf-test and make test-multi targets for BPF activity
  parser integration testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

… mode

Implement interval-gated probabilistic PC sampling that only serializes
kernels during active sampling windows, not for the entire process lifetime.

Architecture:
- CUPTI lifecycle: enable (once) → start/stop (per window) → disable (once)
- Enable START_STOP_CONTROL attribute so start/stop work from CUPTI callbacks
- Collection mode is KERNEL_SERIALIZED for per-kernel correlation
- Probabilistic window: every PARCAGPU_PC_SAMPLING_INTERVAL seconds, roll a
  PARCAGPU_PC_SAMPLING_PROBABILITY die; if it hits, start sampling until the
  window closes, then stop and drain data
- start()/stop() are mutex-guarded and idempotent (no double-start/stop races)
- ctxSynchronize before start to satisfy CUPTI's GPU-idle requirement

Key changes:
- pc_sampling.cpp: Session-based enable with per-window start/stop, semaphore-
  gated stall reason map replay (replaces rate-limited emission), CUPTI 12.4
  ABI version check (v22 correlationId boundary), graceful permission failure
  handling in enable
- cupti.cpp: Probabilistic window state machine in ENTER/EXIT callbacks,
  env var config (probability, interval), env_config validation
- probes.d: Add error USDT probe for surfacing CUPTI failures to BPF
- test/mock_cupti.c: Full PC sampling mock with real cubin from pc_sample_toy,
  real SASS offsets for source-line correlation, 11-entry sample table cycling
  through shmem_bounce/hash_churn/trig_storm kernels
- test/mock_cuda.c: Add cuCtxSynchronize stub
- test/test-pc-mock.sh: New GPU-less test using mock libs and real cubin
- test/test-pc-real.sh: Set probability=1 interval=0.5 for reliable test hits
- test/bpf/: Move CUPTI struct defs to shared cupti_bpf.h, add error event
  handling, CUDA 12.4+ correlationId support
- test/CMakeLists.txt: Build mock CUDA driver library

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

usdt headers now live in parca-dev/usdt and the cupti bpf
headers now live in this project.  So we don't need to vendor
otel anymore.