Alternative logic for solver creation tasks

[jaimergp]

Description

Same as #242 (closes #240) but trying other methods. We have reworked the "conda specs to libsolv tasks" logic to make use of libmamba.Solver.add_pin features now available in 1.5.1 to ensure we don't unnecessarily update packages.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[jezdez]

@jaimergp I concur, this sounds like a good idea. We might be able to package libmamba 1.5.0 ahead of the release as well, of course, to retrofit testing on defaults as well.

[jaimergp]

Some good progress thanks to the pin fixes in main via mamba-org/mamba#2786. We will need a mamba 1.5.1 for that, so expect some failures here.

Note the flags we were using (see e40f0da) are not compatible with solver.add_pin, so I had to remove them (cc @AntoinePrv). Doesn't seem to make a difference so far in conda/conda's test_solve.py.

Let's see what the CI says! 👀

[jaimergp]

Ok, not bad, we are getting closer:

Upstream, 9 failures:

• tests/cli/test_main_clean.py::test_clean_tempfiles - false positive due to flakiness
• tests/cli/test_subcommands.py::test_create - weird networking error?
• tests/cli/test_subcommands.py::test_env_create - weird networking error?
• tests/core/test_solve.py::test_only_deps_2 - passes locally with dev libmamba
• tests/test_create.py::test_install_features- passes on CI (libmamba 1.5.0) but breaks with proper Python pinning. Given it involves mkl features I am inclined to skip it, but 🤷
• tests/test_create.py::test_package_pinning
• tests/test_create.py::test_update_all_updates_pip_pkg
• tests/test_export.py::test_explicit - need bugfix upstream (libmamba 1.5.1?)
• tests/test_export.py::test_export - need bugfix upstream (libmamba 1.5.1?)

Unit, 3 failures:

• tests/test_modified_upstream.py::PatchedCondaTestCreate::test_neutering_of_historic_specs - we fixed this to match conda/conda!
• tests/test_modified_upstream.py::test_python2_update
• tests/test_modified_upstream.py::test_update_all_1

[jaimergp]

tests/test_misc.py::test_explicit_missing_cache_entries fails because PackageCacheData.get_all_extracted_entries()[0].url is None (on macOS only!). I can't reproduce locally, it's not solver-related, and it passes on other operating systems 🤷