Improve dgoss test collection for image types

Ideally, users shouldn't need to be notified for "expected" test skips. For instance, min images simply won't ever run tests that appear in std for Python and R installations. These tests should not only be skipped on min, but shouldn't even show in the test counts for min. By better separating the tests, we should be able to prevent missing unintentional skips should they ever happen.

It could be useful to include the list the skipped tests when the `--verbose` flag is set.

This also makes me think about whether we should break up the tests into sections or files that are included conditionally instead of peppering this everywhere

    skip: {% raw %}{{ if eq .Env.IMAGE_TYPE "min" }}true{{ else }}false{{ end }}{% endraw %}

Originally posted by @bschwedler in https://github.com/posit-dev/images-shared/issues/123#issuecomment-2704258403

Start with the dgoss test definitions and the existing IMAGE_TYPE skip conditions shown in the issue. Compare collection and reporting for min and std images across Python and R installations; done means expected skips no longer appear in min test counts, with verbose skipped-test output considered if the existing test runner supports it.