Semantic Memory Helpers

Helper functions and constants for semantic memory dedupe.

This module keeps validation, ranking, merge, and metadata helper logic out of the main dedupe job orchestration file.

Only names listed in __all__ are intended for reuse by sibling modules. Underscore-prefixed helpers remain shared internal utilities inside the gllm_memory.dedupe package, not part of the broader public package API.

The timestamp metadata subset stays separate from the broader system-metadata set because scan filters and metadata-compatibility checks need direct access to timestamp keys without pulling every system field into that logic.