Apply exemplar's new CI system

[ednolan]

This commit applies the following changes:

• Add bemanproject/infra-workflows as a beman-submodule in .github/workflows
• Add bemanproject/infra as a beman-submodule in infra/
• Copy over the latest CMakePresets.json file from exemplar
• Add an empty lockfile.json to make infra/cmake/use-fetch-content.cmake happy
• Update the ci_tests.yml file to provide CI configurations for GCC 13-15 and Clang 19-20
• Update the badges in the README
• Rename the paper/ directory to papers/

[JeffGarland]

One thing to be aware of @ednolan is that we're currently not supporting MSVC because we still have unique_resource which is dependent on TS impls only available on clang/gcc.

[ednolan]

I think the only thing that changes with respect to MSVC in this commit is that we have MSVC presets in the CMakePresets.json file, but I think it's okay to include those; they aren't run in CI and if users try to use them, they just won't work; I could take them out but I think it's easier to just be consistent with the other presets files and tell users to rely on the README to determine which compilers are supported rather than the list of presets (with eventual CI verification that the set of supported compilers in the README is exactly the set that's tested in CI).

By the way, I determined while working on this commit that this library doesn't support libc++ either, in case that was something you wanted to address.

[JeffGarland]

@ednolan why do you say it doesn't support libc++ -- is that not the default option on Clang? Also to say I routinely compile with clang-19 and clang-20...