Re-Enable fmt module tests, update module-test.cc

[MathewBensonCode]

• Refactor test/CMakeLists.txt to enable testing for modules
• The tests in module-test.cc seem to not have been updated in some time despite changes in the main library.
• Wide String versions of several tests appear to be deprecated so have been commented out.
• Refactored tests related to fmt::format_args that now requires lvalue references as opposed to direct values.
• Tests for items that have since been removed from the library like fmt::is_char and fmt::localtime as far as I can tell
• testing for the fmt::detail namespace. The MSVC github workflow could not differentiate the between the fmt::detail and fmt::v12::detail. Removed windows testing for this

Should close #4698

[MathewBensonCode]

@vitaut, what is the scope of testing that we require for testing the module target?

Do we just want to test the public API or the full API?

The tests for the regular library involve tests for the entire library as they are able to reach into the entire code base.

With the module based library, it brings up the issue of visible and invisible APIs.

In this pull request, Ideally I have just remove the "inner" code(and some outdated code), which is being tested by the regular library anyway, and just test that the expected public functionality works.

I have commented out the bits that would be deleted if we we're to take this approach.

The other approach would be to work out how to work with modules and macro based testing frameworks.

I'm doing some experiments with this, but it may need another pull request as the changes are likely to be drastic, like moving tests into headers, or making the tests part of the module, etc.

[vitaut]

We definitely don't need to test everything. A simple sanity test that exercises a small subset of the API should be sufficient. I would recommend splitting the changes into smaller PRs, e.g. focusing on one compiler (e.g. clang) first.

[vitaut]

That said, we shouldn't delete code from the module test if it is broken with modules. On the contrary - we should keep it as a regression test for the fix. It is OK to conditionally compile it until the fix is available.

[MathewBensonCode]

After further investigation, I have identified that the wide string versions of most tests in module-test.cc were not compiling due to the functionality being deprecated in the main library.

I have just commented them out with explanations in the comments, however, these may be candidates for removal as I observed that they we're not present in the other *-test.cc files.

Compiler Specific testing does not appear to be an issue in this case. The module-test.cc file was well written to only deal with module tests so likely just needed to be updated.

module-test run visible here:

https://github.com/fmtlib/fmt/actions/runs/22850169158/job/66276473337?pr=4702#step:7:1404

[vitaut]

Please apply cmake-format and revert unrelated changes.

[vitaut]

Looks like there are some merge conflicts, please rebase.