fix: avoid FalkorDB edge rematch scans

[mturac]

Summary

Avoids the FalkorDB edge search re-MATCH pattern that scans RELATES_TO edges by uuid after the full-text procedure or BFS path traversal has already produced the relationship.

The full-text path now uses the returned relationship directly, and the BFS path filters path relationships to RELATES_TO before deriving source/target nodes with startNode / endNode.

Type of Change

• Bug fix
• New feature
• Performance improvement
• Documentation/Tests

Objective

Fix the FalkorDB edge search query shape described in #1272 so edge endpoint lookup is linear in the returned relationships instead of forcing a relationship re-scan by UUID.

Testing

• Unit tests added/updated
• Integration tests added/updated
• All existing tests pass

Validation run:

• DISABLE_FALKORDB=1 DISABLE_KUZU=1 DISABLE_NEPTUNE=1 uv run pytest tests/driver/test_falkordb_search_ops.py
• uv run ruff format graphiti_core/driver/falkordb/operations/search_ops.py tests/driver/test_falkordb_search_ops.py --check
• uv run ruff check graphiti_core/driver/falkordb/operations/search_ops.py tests/driver/test_falkordb_search_ops.py
• git diff --check

Breaking Changes

• This PR contains breaking changes

Checklist

• Code follows project style guidelines (make lint passes)
• Self-review completed
• Documentation updated where necessary
• No secrets or sensitive information committed

Related Issues

Closes #1272