fix(lint): resolve all ruff E402/I001/F821 errors

- Move pytestmark after all imports in 35 test files (E402: not-at-top)
- Add TYPE_CHECKING guard for FlightProcessor in composition.py (F821)
- Sort import blocks in src/ and tests/ (I001 auto-fix via ruff --fix)
- ruff check src/ tests/ now exits 0 with no errors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/e2e/test_metrics.py

@@ -3,14 +3,14 @@
 import numpy as np
 import pytest
 
-pytestmark = [pytest.mark.unit]
-
 from gps_denied.testing.metrics import (
     absolute_trajectory_error,
     relative_pose_error,
     trajectory_rmse,
 )
 
+pytestmark = [pytest.mark.unit]
+
 
 def test_rmse_identical_trajectories_is_zero():
     est = np.array([[0.0, 0.0, 0.0], [1.0, 0.0, 0.0], [2.0, 0.0, 0.0]])