refactor: extract scan and factorize functions to separate modules

Create new modules that re-export functions from core.py:
- flox/factorize.py: factorize_, FactorProps, etc.
- flox/reindex.py: reindex_, reindex_numpy, etc.
- flox/scan.py: groupby_scan, chunk_scan, etc.

This improves code organization and provides a clearer API.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: dcherian

flox/factorize.py

@@ -0,0 +1,30 @@
+"""Factorization functions for groupby operations.
+
+This module provides functions for factorizing groupby labels.
+Re-exported from flox.core for backward compatibility.
+"""
+
+from __future__ import annotations
+
+# Re-export from core for backward compatibility
+from .core import (
+    FactorizeKwargs,
+    FactorProps,
+    _factorize_multiple,
+    _factorize_single,
+    _lazy_factorize_wrapper,
+    _ravel_factorized,
+    factorize_,
+    offset_labels,
+)
+
+__all__ = [
+    "FactorizeKwargs",
+    "FactorProps",
+    "_factorize_multiple",
+    "_factorize_single",
+    "_lazy_factorize_wrapper",
+    "_ravel_factorized",
+    "factorize_",
+    "offset_labels",
+]

flox/reindex.py

@@ -0,0 +1,20 @@
+"""Reindexing functions for groupby operations.
+
+This module provides functions for reindexing arrays during groupby operations.
+Re-exported from flox.core for backward compatibility.
+"""
+
+from __future__ import annotations
+
+# Re-export from core for backward compatibility
+from .core import (
+    reindex_,
+    reindex_numpy,
+    reindex_pydata_sparse_coo,
+)
+
+__all__ = [
+    "reindex_",
+    "reindex_numpy",
+    "reindex_pydata_sparse_coo",
+]

flox/scan.py

@@ -0,0 +1,24 @@
+"""Scan operations for groupby reductions.
+
+This module provides scan operations (cumulative reductions) for grouped data.
+Re-exported from flox.core for backward compatibility.
+"""
+
+from __future__ import annotations
+
+# Re-export from core for backward compatibility
+from .core import (
+    _finalize_scan,
+    _zip,
+    chunk_scan,
+    groupby_scan,
+    grouped_reduce,
+)
+
+__all__ = [
+    "_finalize_scan",
+    "_zip",
+    "chunk_scan",
+    "grouped_reduce",
+    "groupby_scan",
+]