Adding RegistryResults and RegistryResource to the registry API

[msdemlei]

This has been found necessary in the context of global discovery (PR #470), but since users are actually handling instances of these classes quite a bit, it seems wise to bless them as parts of the API.

[msdemlei]

Oh, there is a CI failure we might want to fix while we're at it:

157 .. doctest-remote-data::
158
159   >>> from astropy.coordinates import SkyCoord
160   >>> registry.search(registry.Freetext("Wolf-Rayet"),
Differences (unified diff with -expected +actual):
    @@ -5,3 +5,3 @@
     ------------------------------- ...
     ivo://cds.vizier/j/a+a/688/a104 ...
    -   ivo://cds.vizier/j/aj/166/68 ...
    +  ivo://cds.vizier/j/apj/938/73 ...

I am a bit surprised that a resource vanishes here (apparently, its spatial coverage changed), but that new resources come up here is fairly expectable. if the matching language is rich enouch, I'd say "make sure ivo://cds.vizier/j/a+a/688/a104 is in the list" would be fine, else perhaps we should ignore the output?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.85%. Comparing base (029980e) to head (4706df9).
Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #608      +/-   ##
==========================================
+ Coverage   81.70%   81.85%   +0.15%     
==========================================
  Files          69       70       +1     
  Lines        7093     7160      +67     
==========================================
+ Hits         5795     5861      +66     
- Misses       1298     1299       +1     

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[bsipocz]

if the matching language is rich enouch, I'd say "make sure ivo://cds.vizier/j/a+a/688/a104 is in the list

We should be able to do a partial matching with an ellipse after the first result line. If that doesn't work, IGNORE_OUTPUT is indeed the way to go.

[bsipocz]

These need to be imported, too.

And that should fix the traceback in the docs build.

[bsipocz]

Ignore the changelog and milestone check statuses, I'm still thinking about which release to put this in and if it can be joined with other API cleanup PRs.

[bsipocz]

Thank you Markus!