Unit tests for talon.nvim

[saidelike]

It would be nice to have unit tests to avoid regressions etc. They could be similar to cursorless.nvim since it is also an extension but will be focused on lua (whereas cursorless.nvim is mainly node but also lua, see cursorless-dev/cursorless#2374)

• https://hiphish.github.io/blog/2024/01/29/testing-neovim-plugins-with-busted/

[fidgetingbits]

Actual busted tests cursorless PR saidelike/cursorless#7 for quicker future reference. It would be good to add tests for #8 once we decide what behavior we want.