Add delete_where() API for bulk index deletion by filter

Summary

Add delete_where() / adelete_where() to delete index documents by filter expression, and refactor clear() to share the same internals.

Level: Intermediate

Current State

• clear() deletes all documents via batched FilterQuery("*") flow.
• drop_documents() / drop_keys() only delete known IDs/keys.
• There is no public API to delete a filtered subset of index documents.

Proposed Change

• Add:
  • delete_where(filter_expression, batch_size=500) -> int
  • adelete_where(filter_expression, batch_size=500) -> int
• Refactor both clear() and delete_where() to use shared private internals:
  • common batch-ID fetch loop
  • existing _delete_batch() and async equivalent as delete primitive
• Implement clear() as delete_where(FilterExpression("*")).

Definition of Done

• Filtered bulk deletion works on standalone and cluster clients.
• clear() delegates to the shared deletion internals (no duplicated batch loop).
• Integration tests cover selective match, no-op match, and full-clear behavior.
• Docs include one usage example.

Out of Scope

• Hard-delete audit logging or soft-delete support.

Start by locating the existing clear(), drop_documents(), drop_keys(), and _delete_batch() entry points, including their async equivalents. Run the integration tests for deletion behavior first, then cover selective matches, no-op matches, and full clears for standalone and cluster clients. Done means both new APIs work, clear() shares the deletion internals, and the docs contain one usage example.