improve schema info collection combiner handling

[braingram]

Description

schema_info currently fails to find both subschemas and attributes of subschemas for schemas that use certain "combiners" (like allOf) and/or references.

This PR updates schema_info to support more schema configurations (including $ref and allOf usage).

Requires spacetelescope/rad#525 as the rad schemas contain invalid extra $ref items.

Tasks

• run pre-commit on your machine
• run pytest on your machine
• Does this PR add new features and / or change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • update relevant docstrings and / or docs/ page
  • for any new features, add unit tests

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: bug fix
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.general.rst: infrastructure or miscellaneous change

[braingram]

Specutils error comes from a bug in gwcs with astropy 7 that is fixed in the development version but not yet released.

The weldx failure is from weldx pinning asdf to <4.

One thing to consider with this PR is that the changes will (correctly) cause schema_info to not pick up archive_catalog info for old rad schemas (non-development versions, see spacetelescope/rad#525). The latest released version of rad has an asdf upper pin for <4. So as long as we merge and release this before the next rad release and add a rad pin for >= 4.0.1 (if 4.0.1 is the asdf release version) we should avoid issues.