Implement command CSFixUsings

[StefanFanaru]

I've added a nvim user command that allows you to remove all unecesarry using directives from the current buffer.
:CSFixUsings

You can set it up with conform.nvim to be executed every time you format the buffer:

{
	"stevearc/conform.nvim",
	keys = {
		{
			"<leader>f",
			function()
				require("conform").format({ async = true, lsp_fallback = true })
				if vim.bo[0].filetype == "cs" then
					vim.cmd("CSFixUsings")
				end
			end,
			mode = "",
			desc = "[F]ormat buffer",
		},
	},
	(...)
}

And/or you can set it up to run automatically when you write your buffer

vim.api.nvim_create_autocmd("BufWritePre", {
	pattern = "*",
	callback = function(args)
		if vim.bo[0].filetype == "cs" then
			vim.cmd("CSFixUsings")
		end
		-- optional, if you use conform and want this
		require("conform").format({ bufnr = args.buf })
	end,
})

Waiting for your feedback.