Problem: plugins that don't use devicons have no way to get nonicons
glyphs for files. The only integration path is the devicons
monkey-patch via apply().
Solution: add get_icon(name, ext) and get_icon_by_filetype(ft) to
the public API in init.lua. Both use lazy require of the resolve
module and return nil on miss so callers decide fallback. Document
both functions in vimdoc and update the oil.nvim recipe.
Problem: the original ya2s/nvim-nonicons fork diverged enough that
maintaining it as a fork was pointless. The set_icon() approach broke
with modern nvim-web-devicons, and the extensions directory coupled
integrations that belong in user config.
Solution: from-scratch rewrite with function wrapping + table mutation
override engine, vim.g.nonicons config pattern, vendored mapping with
integer codepoints, health check, vimdoc with recipes, and no built-in
plugin integrations.
