UN-2862 [FIX] Remove legacy QUEUED and CANCELED statuses
- Remove QUEUED and CANCELED enum values from ExecutionStatus
- Remove legacy status mappings from 4 worker status mapping files
- Remove dead LEGACY_STATUS_MAPPING dict (never used)
- Remove unreachable QUEUED/CANCELED mappings from callback tasks
- Fix unused QUEUED default parameter to PENDING in internal_client
- Add human-readable labels to ExecutionStatus.choices using .title()
- Remove unmigrated API constraint from file_execution model
All legacy status references cleaned up while maintaining backward compatibility
through string-based legacy mappings in callback tasks.
Co-authored-by: harini-venkataraman <115449948+harini-venkataraman@users.noreply.github.com>