Push-to-talk + pynput fixes

This pull request adds a few input-related features and fixes:

Support for held hotkeys (add_held_hotkey()).
RECORD_HOTKEY can alternatively be held down to record until it is released (push-to-talk).
The time the hotkey waits to detect a double tap for clipboard usage no longer delays the start of recording, making it more responsive.
Support for unbound hotkeys (set to None). Both the new hotkeys are set to None by default. Unbound hotkeys will not be listed in the terminal.
Fixes to pynput (Linux/Mac).
- Support overlapping hotkeys: Can bind Shift+Ctrl+R to one thing and Shift+R to another, and then trigger the first without also triggering the second.
- Support for many more keys like Space, Capslock, Esc, F-keys, etc.

PynputHandler has been largely rewritten, because to support this stuff I needed to move away from using GlobalHotKeys().

With this I think pynput on Linux/Mac should be functionally equivalent to the keyboard package on Windows, except for key suppression.

ILikeAI / AlwaysReddy