feat: enable stale annotation cleanup during db import

[PALLAVIKHEDLE]

Summary

• Enable stale annotation cleanup by setting clean_up_siblings = True on AnnotationImporter and implementing get_filters() to scope cleanup by tomogram_voxel_spacing_id.
• Add StaleAnnotationDeletionDBImporter class (already referenced by StaleVoxelSpacingDeletionDBImporter but was missing).
• Fix and unskip test_import_annotations_files_removes_stale test, and update populate_stale_annotations fixture to include tomogram_voxel_spacing_id.

Context

Previously, stale annotation cleanup was disabled because annotations were only associate with runs, but the importer searched for annotations within a voxel spacing. Now that tomogram_voxel_spacing_id has been added (#641), we can safely filter annotations by voxel spacing and clean up stale ones.