add adversarial tests for node_id_occupancy_update and callees

22 tests in new test_intrusive_misc.c covering:
- node_id_occupancy_reset/update (early exits, collision reroll,
  probabilistic purge, TX purge on collision)
- exhaustive zc=1 sweep (127 sub-cases) and 1000-iteration
  random property test

9 tests added to test_intrusive_util.c covering:
- bitmap_set/bitmap_test (boundaries, round-trip, idempotency)
- random (bound edge cases, range exhaustive)
- chance (deterministic edges, statistical)

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

Author: pavel-kirienko

tests/CMakeLists.txt

@@ -102,6 +102,7 @@ gen_test_matrix(test_intrusive_tx "src/test_intrusive_tx.c")
 gen_test_matrix(test_intrusive_rx "src/test_intrusive_rx.c")
 gen_test_matrix(test_intrusive_rx_admission "src/test_intrusive_rx_admission.c")
 gen_test_matrix(test_intrusive_rx_session "src/test_intrusive_rx_session.c")
+gen_test_matrix(test_intrusive_misc "src/test_intrusive_misc.c")
 # API tests.
 gen_test_single(test_api_tx "${library_dir}/canard.c;src/test_api_tx.cpp")