Use udev symlinks instead of event file paths

[Lxtharia]

These changes should help with the problem, that the /dev/input/eventXX file for a device might be different after a reboot (see https://wiki.archlinux.org/title/Udev)

This issue was mentioned in #34 and @triplefox proposed steps on how to tackle this problem:
#34 (comment)

Even though there might even be a way to do this without udev, I've stuck with it, as it's needed for the systemd service anyway.

The main idea is to prompt a user for a explicit device name (instead of using event23 for example)
and then let udev create a symlink like /dev/numpad -> /dev/input/eventXX automatically on boot.
To do this, udev needs some way of identifying a device.
I've decided to use the ATTRS(phys) attribute.
The steps are now as follows:

1. User creates new device keebie -n and gets prompted for a name (f.e. numpad1)
2. The current event file is recognized as usual by pressing a key on the device (f.e. /dev/input/event23)
3. The ATTRS(phys) is read from that device (via evdev)
4. This attribute is used in the udev rule that will symlink the device to /dev/numpad1
   • A symlink is created for the current session so the user doesn't need to reboot

A configuration file looks now like this:

{
   "initial_layer": "default.json",
   "devFile": "/dev/numpad",
   "udev_match_keys": [
      "ATTRS(phys)==\"usb-0000:0a:00.3-2/input0\""
   ],
   "udev_rule": "85-keebie-numpad.rules"
}

I have not tested it much, but I will do so in the next few days. Still wanted to open the PR now for feedback.

[Lxtharia]

Using the phys attribute somehow broke for me once, so this might not be the ultimate unique identifier.
Maybe using the vendorId + productId is a better option for the udev rule?