refactor!: remove nvim-treesitter dependency

[amaanq]

This will make the plugin solely depend on vim.treesitter which might need users to be on 0.9.0 at least - but in the near future nvim-treesitter will deprecate most of its plugin functionality and only serve as a parser installer, this PR will prepare for that. You can read about it more in the new main branch in nvim-treesitter

Do thoroughly go through it and critique is welcome, I also tidied up some of the code docs for types/function params

[cshuaimin]

Thank you very much! I didn't know vim.treesitter can do ft -> lang translation.

Some nits:

• you can use ts instead of vim.treesitter
• vim.bo[buf].filetype instead of nvim_get_option_value()

[cshuaimin]

Thank you again. I fixed the CI and parser check.

[amaanq]

awesome, thanks!