refactor(eventsub): generate entire files

[Nerixyz]

This refactors the generation of the JSON parsing to happen at build time and at whole file level. There are two advantages: (1) we can utilize modern processor capabilities and generate multiple files simultaneously (multithreading) and (2) we can make our build system happy, which only knows about whole files (and their timestamps).

One important goal is that building the deserializers is optional (i.e. if someone doesn't have libclang, or it can't parse a TU, the build should still work).

When configuring, we do the following:

• Check if python3 is available (not required)
  • Set up a virtual environment (venv) in the build directory and install the required dependencies
  • Test that clang is able to parse a simple translation unit that includes boost, Qt, and a standard library header.
• For each header that is specified to generate_json_impls, the corresponding source and include paths are computed
• If the generation is supported
  • Add a target for each source file that generates that file (add_custom_command)
• Add all source files to the twitch-eventsub-ws target (in both cases, however, if generation is supported, these files will have a dependency on the previously generated target)

In CI, we generate on Ubuntu-24.04 and Windows (where FORCE_JSON_GENERATION=On). I'm not sure why this fails on macOS, even with llvm installed (seems like it can't find Qt headers).

[pajlada]

Small note, but this seems like a good approach

I don't like reading the extra cmake code but it is what it is

[pajlada]

Works as expected on my machine, thank you!

[camporter]

After rebasing on top of master, the freebsd builds are very slow. It seems like this is because there's no freebsd wheels for clang-format and other requirements?

[pajlada]

After rebasing on top of master, the freebsd builds are very slow. It seems like this is because there's no freebsd wheels for clang-format and other requirements?

I added an option to skip it entirely SKIP_JSON_GENERATION, should be fixed with #5904