feat!: include the sender ID in static messages

[sxyazi]

In practice, the severity of static messages has proven to be meaningless and increases protocol complexity.

This PR replacing severity with sender to resolves #1004 (comment)

⚠️ Breaking changes

This PR removes the ps.pub_static() method and replaces it with ps.pub_to():

- ps.pub_static(10, "greeting", "Hello, World!")
+ ps.pub_to(0, "@greeting", "Hello, World!")

Messages with a kind that starts with @ indicate they are static messages. Accordingly, ps.sub_remote() subscribes to static messages using that kind:

- ps.sub_remote("greeting", function() end)
+ ps.sub_remote("@greeting", function() end)

The ya pub-static command has also been removed and replaced with ya pub:

- ya pub-static 10 "greeting" --str "Hello, World!"
+ ya pub "@greeting" 0 --str "Hello, World!"

[sxyazi]

Need more tests to merge

[mikavilpas]

Looks like a great idea, and this would be quite helpful in the neovim integration. I'll try to find time to do a proof of concept with this, maybe next week.