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)

tests/api/auth/test_login.py

@@ -34,14 +34,14 @@ async def test_login_failure(client: httpx.AsyncClient) -> None:
     )
     assert response.status_code == 401
 
+@pytest.mark.anyio
+@pytest.mark.fuzz
 @pytest.mark.anyio
 @settings(**_FUZZ_SETTINGS)
 @given(
     username=st.text(min_size=0, max_size=2048),
     password=st.text(min_size=0, max_size=2048)
 )
-
-@pytest.mark.anyio
 async def test_fuzz_login(client: httpx.AsyncClient, username: str, password: str) -> None:
     """Fuzz the login endpoint with random strings (including non-ASCII)."""
     _payload: dict[str, str] = {"username": username, "password": password}