Support for test Timeouts

[FourierTransformer]

• Pure Lua would only be able to handle non-blocking timeouts, but maybe that's good enough for now.
• Would need something else (lanes?) for blocking timeouts. Might also be useful to spread the load to run as many test files as possible. I feel like it should be an optional dependency

[FourierTransformer]

Yeah, the more I think about this, ensuring the main test runner code is pure Lua may help folks out if they want to run this in more places. Currently the couple of C libraries are only used in main.tl for file path shenanigans. So, "lanes" should be more optional in that regard.

[FourierTransformer]

I think long term, I want to bundle-out a smaller single-file version that allows people to just run a test file on its own with no required dependencies. It wouldn't have all the bells and whistles, but it would allow folks to run tests anywhere Lua runs.