feat: add --check_format=json|pretty

[lewis6991]

Adds a new CLI option --check_format which accepts the values: 'json'
(current behaviour), and a new 'pretty' value which prints a colorized
human readable report to stdout, similar to common compilers and
linters.

Results are printed with color unless NO_COLOR is defined in the users
environment, as per https://no-color.org.

If --check_out_path is provided, then the results are always saved to
file regardless of the --check_format value.

I've made pretty the default format, however to mitigate against any breakage I've made it also write the json files with --check_out_path is provided, so this will be like enabling both formats at once.

Other changes

• Outlined some functions in check_worker.lua.
• Made --quiet work properly with --num_threads

[lewis6991]

Example:

[mikesmithgh]

I'm not sure if it makes sense in the scope of this. But it would be nice to return a nonzero exit code if results are found for CI builds to fail.

If it is helpful, I recently did something similar for a Neovim plugin https://github.com/mikesmithgh/kitty-scrollback.nvim/blob/main/scripts/internal/__lua_language_server_check.lua

[lewis6991]

First commit after the last release has already added this.

[mikesmithgh]

awesome 9f25c27 yep I see it 🙌. Thanks!

[tomlau10]

great work 👍
and I just tested it on windows and found some small issues

[jeffzi]

Great addition! I had previously built a tool to process diagnosis files with similar formatting (see llscheck). Here's how it looks in my implementation:

A couple of suggestions to enhance the output format:

1. For the summary line, consider including a breakdown by diagnostic severity. For example:
   "Total: 4 (3 Warnings, 1 Hint) across 2 files"
2. To improve readability with multiple files, you could add file headers with per-file diagnostic counts (see screenshot above).

That said, I find your diagnostic line formatting clearer than my implementation. Feel free to use parts of my code if that helps.