fix: prevent premature loading of which-key.nvim

[bbnolauv]

Problem

The recent fix #155 introduced pcall(require, "which-key.state"). However, when using package managers like lazy.nvim, calling require on a lazy-loaded plugin's module will immediately force-load the plugin on the very first keystroke, bypassing any user-defined lazy-loading configurations (e.g. cmd, keys, or event for which-key).

Solution

Instead of directly calling require, check package.loaded["which-key.state"] ~= nil first.

This prevents lazy.nvim's global require hook from intercepting the call and loading the plugin prematurely. If which-key is already loaded, we then safely perform the require as before.