Make FMT_STRING redundant when FMT_USE_CONSTEVAL is enabled

[friedkeenan]

Closes #4611.

As discussed in that issue, FMT_STRING(s) has been made to simply expand to s when FMT_USE_CONSTEVAL is enabled.

This fixes the issue with formatting chrono durations.

[vitaut]

Thanks for the PR! Please move the check to FMT_STRING because FMT_STRING_IMPL is also used in format string compilation which we shouldn't change.

[friedkeenan]

Moved the check. I'm not certain how concerned I should be about the failing tests on the previous commit. Running the tests locally succeed for me, at least

[friedkeenan]

I'm not really sure what to make of the failing workflows. The linting stuff really doesn't seem like my fault. The other failing ones though do seem related to FMT_STRING, but I'm not sure what to make of the errors. Could it be that FMT_USE_CONSTEVAL is getting enabled when it shouldn't be? Sorry, I'm not very familiar with the codebase.

[vitaut]

Most (possibly all) of the issues should be fixed now. Could you rebase?

[friedkeenan]

Rebasing seems to have gone okay. I've never actually done it before since I prefer to merge, but should be done now.

[vitaut]

There is still a lint issue caused by clang-format version mismatch. You can ignore it.

[friedkeenan]

Everything else seems to be passing. Good to merge, then?

[vitaut]

Merged, thank you!