Reinstate evdev-based key handling

[TTWNO]

• Use generic version of serde_json
• fmt
• Cleanup using macro
• Make mode an exaustive enum
• Update events struct to work like Command does
• Spawn new task for input events
• Update services to handle input events
• Use new input event handlers
• Update cargo lock
• Add input server binary
• Update cargo lock

[TTWNO]

Instructions on testing:

# in Odilia root directory
$ cargo run
# in another terminal, in the input-server/ directory
# your user must be in a group which is allowed to read evdev
$ cargo run

Now press capslock+g to send the "stop speech" command. This should make the TTS say "stop speech, eh!"