feat(command): expose plugin suggestion callbacks

[NicDevTV]

Description

Adds WIT support for plugin-provided command suggestions.

This introduces suggestion request/result types and a new command-node hook so plugins can attach server-side suggestion handlers to command arguments. The plugin world now exports handle-command-suggestion, allowing Pumpkin to ask the plugin for completions when a Java client requests minecraft:ask_server suggestions.

This is needed for plugin commands with custom argument grammars, such as weighted block patterns like 50%stone,50%dirt, where normal block-state completion is not enough because only the active pattern segment should be replaced.

Testing

• Consumed by the Pumpkin implementation in the dependent PR
• cargo check -p pumpkin-plugin-api
• cargo check -p pumpkin

[vyPal]

LGTM, please fix merge conflicts

[NicDevTV]

I will asap when I’m back from vacation in 7 days @vyPal