feat(python): expose index cache size (#655)

This is to enable https://github.com/lancedb/lancedb/issues/641.
Should be merged after https://github.com/lancedb/lance/pull/1587 is
released.

python/tests/test_db.py

@@ -301,6 +301,7 @@ def test_replace_index(tmp_path):
         num_partitions=2,
         num_sub_vectors=4,
         replace=True,
+        index_cache_size=10,
     )