Apply ruff-format fixes to unblock CI

Two pre-existing formatting violations were unmasked by the current
CI ruff version: a multi-line raise in discrete_state_transitions.py
(from cd2729d) and a multi-line method signature in
test_predict_covariate_transitions.py (latent from 4131d8f). Both are
mechanical ruff-format outputs with zero behavioral impact.

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

Author: edeno

src/non_local_detector/discrete_state_transitions.py

@@ -395,9 +395,7 @@ def estimate_stationary_state_transition(
             f"got shape {prior_weight_arr.shape}"
         )
     if np.any(prior_weight_arr < 0):
-        raise ValueError(
-            f"prior_weight must be non-negative, got {prior_weight_arr}"
-        )
+        raise ValueError(f"prior_weight must be non-negative, got {prior_weight_arr}")
 
     # p(x_t, x_{t+1} | O_{1:T})
     joint_distribution = estimate_joint_distribution(

src/non_local_detector/tests/models/test_predict_covariate_transitions.py

@@ -114,9 +114,7 @@ def test_mismatched_covariate_length_raises_valueerror(
         with pytest.raises(ValueError, match="time steps"):
             _validate_covariate_time_length(predicted, decode_time)
 
-    def test_matching_covariate_length_passes(
-        self, nonstationary_transition_artifacts
-    ):
+    def test_matching_covariate_length_passes(self, nonstationary_transition_artifacts):
         """When covariate and decode time match, no error is raised."""
         from non_local_detector.models.base import _validate_covariate_time_length