test: fix async fixture isolation, add fuzz marks, parallelize with xdist

- Rebuild repo.engine and repo.session_factory per-test using unique
  in-memory SQLite URIs — fixes KeyError: 'access_token' caused by
  stale session_factory pointing at production DB
- Add @pytest.mark.fuzz to all Hypothesis and Schemathesis tests;
  default run excludes them (addopts = -m 'not fuzz')
- Add missing fuzz tests to bounty, fleet, histogram, and repository
- Use tmp_path for state file in patch_state_file/mock_state_file to
  eliminate file-path race conditions under xdist parallelism
- Set default addopts: -v -q -x -n logical (26 tests in ~7s)

pyproject.toml

@@ -43,6 +43,10 @@ decnet = "decnet.cli:app"
 
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
+addopts = "-m 'not fuzz' -v -q -x -n logical"
+markers = [
+    "fuzz: hypothesis-based fuzz tests (slow, run with -m fuzz or -m '' for all)",
+]
 filterwarnings = [
     "ignore::pytest.PytestUnhandledThreadExceptionWarning",
     "ignore::DeprecationWarning",