fix: resolve mypy type errors in imputation and mimic_iii

- Assert time_col is not None in _fill_with_gap_mask to narrow str|None
- Annotate read_kwargs as dict[str, object] to satisfy type-arg check

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

Author: chaitanyakasaraneni

clinops/ingest/mimic_iii.py

@@ -553,7 +553,7 @@ def _load(self, table_name: str) -> pd.DataFrame:
         path = self._resolve_path(table_name)
         logger.debug(f"Loading MIMIC-III {table_name} from {path}")
 
-        read_kwargs: dict = {}
+        read_kwargs: dict[str, object] = {}
         if self._cfg.chunk_size and table_name in {"chartevents", "labevents"}:
             read_kwargs["chunksize"] = self._cfg.chunk_size
 

clinops/temporal/imputation.py

@@ -210,6 +210,7 @@ def _fill_with_gap_mask(
         entity group, preventing values from propagating across entity
         boundaries (e.g. across patients or admissions).
         """
+        assert self.time_col is not None  # callers guard this
         if self.id_col and self.id_col in df.columns:
             parts = []
             for _, grp in df.groupby(self.id_col, sort=False):