feat: support watching files for changes

[UtkarshVerma]

Is your feature request related to a problem? Please describe.
For some reason, watching the source file for changes does not rerun the corresponding tests. It works for Rust projects, though, which leads me to believe that this is related to this plugin.

Describe the solution you'd like
Marking a file to be watched should rerun tests whenever changes occur.

Describe alternatives you've considered
N/A

Additional context
https://github.com/nvim-neotest/neotest?tab=readme-ov-file#watch-tests

[lawrence-laz]

Seems like a cool feature. Not sure how neotest implements it and how difficult it would be to adapt it to zig. I might look into this at some point, but no promises for now.