Fix P3 code review issues: unused import and type alias

- Remove unused `_generate_bootstrap_weights_batch` import from staggered.py
- Move `PrecomputedData` type alias outside TYPE_CHECKING block in
  staggered_aggregation.py for runtime type hint accessibility

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: igerber

diff_diff/staggered.py

@@ -26,7 +26,6 @@
 from diff_diff.staggered_bootstrap import (
     CSBootstrapResults,
     CallawaySantAnnaBootstrapMixin,
-    _generate_bootstrap_weights_batch,
 )
 from diff_diff.staggered_aggregation import (
     CallawaySantAnnaAggregationMixin,

diff_diff/staggered_aggregation.py

@@ -5,7 +5,7 @@
 group-time average treatment effects into summary measures.
 """
 
-from typing import Any, Dict, List, Optional, Set, Tuple, TYPE_CHECKING
+from typing import Any, Dict, List, Optional, Set, Tuple
 
 import numpy as np
 import pandas as pd
@@ -15,9 +15,8 @@
     compute_p_value,
 )
 
-if TYPE_CHECKING:
-    # PrecomputedData is a Dict[str, Any], but we define the alias here for clarity
-    PrecomputedData = Dict[str, Any]
+# Type alias for pre-computed structures (defined at module scope for runtime access)
+PrecomputedData = Dict[str, Any]
 
 
 class CallawaySantAnnaAggregationMixin: