Add new cross-match catalogs

[jeanconn]

Description

• add the new external catalog integrations and the supporting cross-match logic
  for ICRF3, RFC, GaiaAGN, GaiaQSO, GaiaVarStar, MilliquasGaia, and
  DESIV161
• add the astromon_23 through astromon_27 match sets that use those catalogs (though we may not keep any of these)
• route catalog caches and archive data under ASTROMON_DATA_DIR
• keep test data out of the production cache location
• update the catalog-data scripts and docs to match the new sources and cache layout
• remove local smoke tests that depended on preexisting cache state

Interface Impacts

• cache and archive locations move under ASTROMON_DATA_DIR

Testing

• adds and expands unit tests for the new catalog getters, DESI deduplication,
  cache behavior, match-set definitions, and the catalog data pipeline wiring

Migration

• after the full stack is approved and merged, either move existing caches under
  ASTROMON_DATA_DIR or rebuild them there

Unit tests

• No unit tests
• Mac
• Linux
• Windows

Independent check of unit tests by [REVIEWER NAME]

• [PLATFORM]:

Functional tests

No functional testing.