Pull request #1924: PIPE-3193: Refactor `select_tsys_field` identifier handling
Merge in PIPE/pipeline from PIPE-3193-clone-pipe-3175-pr2 to main
* commit '6e0dbf6d7de09c39ce9ba1db0cf9010fb1001dd0': PIPE-3193: Add test case for numeric field names with CASA-convention auto-quoting PIPE-3193/PIPE-3175: Refactor `select_tsys_field` identifier handling
PIPE-3193/PIPE-3175: Refactor `select_tsys_field` identifier handling
- handle case of `tsys_fields`` specified by index instead of name
- align `src_by_name` keys with Field.name auto-quoted form
- split numeric/name logic branches explicitly
- deterministic tie-breaking in the fallback nearest field selection