Fix :latest checker version resolution for compliance-checker >= 6.0.0

[swarnaleem]

compliance-checker v6.0.0 removed the :latest alias. Before this, CheckSuite.checkers had keys like cf:latest alongside cf:1.11. Now it only has the explicit version. Since esgf-qa was passing cf:latest directly to CheckSuite.run_all(), users on CC >= 6.0.0 would hit:

KeyError: 'cf:latest'

making esgf-qa completely broken unless the exact installed version is passed explicitly (e.g. -t cf:1.11).

The fix moves the :latest resolution into esgf-qa itself. The existing get_installed_checker_versions() already loads all registered checkers and builds a sorted list of available versions per checker name. A new resolve_latest_version() function uses that to map "latest" to the actual highest installed version number before the checker strings are handed off to compliance-checker. So -t cf, -t cf:latest, -t wcrp_cmip6:latest all continue to work as before.

A couple of related fixes are included:

• get_checker_release_versions() had check_suite.checkers.get(checker, "unknown version")._cc_spec_version which crashes with AttributeError when the key isn't found (since .get() returns the fallback string). Now it falls back to finding the highest versioned key for that checker name.
• The "cc6:latest" in checker string check in run_compliance_checker() was hardcoded and would break once versions are resolved. Changed to checker.split(":")[0] in ("cc6", "mip").

Known pre-existing failures

test_args5 and test_args6 were already failing before this change. They fail because the wcrp-data-checker plugin's sanitize() function does not handle numpy.datetime64, so consistency output files are never written and Part 2 of the QA run fails.

Edit:

• Resolves Incompatibility Issue Between esgf-qa and compliance-checker v6.0.0 Due to Removed :latest Alias #23

[sol1105]

Thanks for the update. After looking more deeply into the compliance-checker lookup behavior, :latest was always only an alias for an unversioned checker selection, so eg. cc6:latest was always treated internally same as cc6 and I think we should do the same here.

To sum up, I think the best approach for us is:

• still allowing :latest, but internally in that case use unversioned checker names
• let compliance-checker handle latest-version selection, instead of doing that ourselves