feat(lsp): add snippet support and refactor completion into Item class

lua/lsp/kind.lua

@@ -56,17 +56,16 @@ local DEFAULT_HIGHLIGHTS = {
     Reference = "Special",
 }
 
---- Look up icon and highlight group for an LSP CompletionItemKind number.
----@param kind integer?
----@return string icon  empty string if the kind is unknown
----@return string? hl  nil if the kind is unknown
+---@param kind? integer
+---@return string? icon
+---@return string? hl
 function M.get(kind)
     if not kind then
-        return "", nil
+        return nil, nil
     end
     local name = vim.lsp.protocol.CompletionItemKind[kind]
     if not name or not M.ICONS[name] then
-        return "", nil
+        return nil, nil
     end
     return M.ICONS[name], "OwLspKind" .. name
 end