feat: add max_traversed_entries option

[gregorias]

At my work, we have a huge monorepo with a directory with over 70k entries. This plugin, being synchronous, was blocking Neovim for tens of seconds.

This option should be universally useful to just time-box any search done by this plugin. I don't think it makes sense to leave this search unbounded as people expect interactivity from Neovim.

Perhaps, some change of API will make it possible to make search more optimal (e.g., a batch fetch), but even than a limit to how many entries Neovim has to process is relevant.