fix(tests): prevent xdist worker OOM from leaked tarpit asyncio task

asyncio_default_fixture_loop_scope was 'module', so all async tests in
a module share one event loop. test_lifespan_startup_and_shutdown patched
log_ingestion_worker/log_collector_worker/attacker_profile_worker but not
tarpit_watcher_worker — the real while-True coroutine was created as an
asyncio task on the shared loop and never cancelled. The xdist worker ran
for 4+ hours (confirmed via py-spy + etime=04:48) consuming 15+ GB before
OOM-kill.

Fixes:
- Patch tarpit_watcher_worker in both TestLifespan tests
- Change asyncio_default_fixture_loop_scope to 'function' so each test
  gets its own loop; tasks cannot outlive their test
- Add loop_scope='module' to precision_engine which legitimately needs
  a module-scoped event loop

tests/ttp/rule_precision/conftest.py

@@ -102,7 +102,7 @@ def compiled_rules() -> list[CompiledRule]:
     return _load_compiled_rules()
 
 
-@pytest_asyncio.fixture(scope="module")
+@pytest_asyncio.fixture(scope="module", loop_scope="module")
 async def precision_engine(
     compiled_rules: list[CompiledRule],
 ) -> RuleEngine: