Introduce command lookup

[piotrooo]

Context

Important

Before we can revisit the available options for commands, we need to have a robust solution for command registration and lookup — even when commands are nested.

Let's imagine the following input:

shell:> cmd sub-cmd1 sub-cmd2 arg1 arg2

So where is the full command path? How can it be distinguished from positional arguments (arg1, arg2)?
It’s crucial to have a reliable mechanism for registering and looking up commands.

Nested commands are also a very useful feature, so we need to support them as well.

What changed

• Introduced the CommandTree.Node structure for registering commands, which enables proper command lookup. The tree structure organizes commands in a parent–child relationship, with the executable command located at the leaf.

(root)
  ├── (one)    -> command "root one"
  └── (child)  -> command "root child"
        ├── (first)  -> command "root child first"
        └── (second) -> command "root child second"

• Added the ElementType.TYPE target to the @Command annotation to support sub-commands.
• Removed the ability to define multiple command names in the @Command annotation, as a command name should naturally be a single word (although a name such as "cmd other-word" is still possible).
• When the command name (@Command(name = "cmd")) is not specified, the method name is used as a fallback.
• Refactored CommandOption as record.
• Reverted the .editorconfig file to help developers with differently configured IDEs (spaces vs. tabs).