fix!: i_<C-o>gcc inserts g@$

[numToStr]

Now g@ is returned from the RHS callback of every operator-mode keybindings i.e., gc[motion], gcc etc.. Instead of using a command we are now using a callback as the RHS and returning g@ from that callback to used as an expression, which will be executed by neovim using { expr = true } option. <Plug> mappings are also covered in this fix.

• Before

vim.keymap.set('n', 'gc', '<CMD>lua require("Comment.api").call("toggle.linewise")<CR>g@')

• After

vim.keymap.set('n', 'gc', require("Comment.api").call("toggle.linewise", "g@"), { expr = true })

This PR also changes the .call() method signature, now it returns a function which is used to create keymap RHS

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Fixes #143