[POC] Command Registration

[st0012]

Benefits

Extensible

Users or gems will be able to register new commands with:

DEBUGGER__::Session.register_command("foo", aliases: ["fo"]) do |arg|
  # my command
end.document category: "My Gem", content: <<~MD
  * foo does blablabla
MD

And then the command document will appear in the help

❯ ruby -Ilib -rdebug target.rb
[4, 9] in target.rb
     4|   # my command
     5| end.document category: "My Gem", content: <<~MD
     6|   * foo does blablabla
     7| MD
     8|
=>   9| binding.b
=>#0    <main> at target.rb:9
(rdbg) help foo    # command

### My Gem

* foo does blablabla
(rdbg)

Easier to maintain

Currently, command documents need to be written in Ruby comments with a strict format. And the parsing logic is quite adhoc for that reason. With this approach, we can simplify the parsing logic and make the document naturally a part of the command definition.

Additional thoughts

• The CommandSet logic is a replication of the Config class, which prevents sharing mutable hash while allowing modifying values. I hope this will make it Ractor-safe?