Improve keybinding handling

[alexgaribay]

This PR does some improvements to the key handling of the LeaderPopup.

Here's a list of the main changes:

• Whenever the config is loaded, a map is generated for each config keybinding so it's not generated during popup initialization
• Key presses are immediately intercepted as soon as LeaderAction is invoked and stored in a buffer to be processed once the UI has finished rendering (addresses Keypresses before the popup are not registered, popup is slow #23)
• In the process of changing how key presses are managed, arrow keys can be used to navigate (addresses Request support for the arrow keys. #20)

Please note that I'm not a Kotlin developer nor do I have experience with Swing. These changes were made with Claude 3.7 with very targeted prompts on the interactions and the issues I was trying to solve.