llm schemas dsl debug command

[simonw]

Simple command to turn a DSL schema into JSON.

Inspired by:

• Add nested array and object support to the schema DSL #792
• Implement a concise schema DSL alternative to JSON schema #790

[simonw]

Documented at bottom of this section: https://github.com/simonw/llm/blob/9a3802121869ead73538da596f6be9861e670b30/docs/schemas.md#alternative-schema-syntax

And here on --help: https://github.com/simonw/llm/blob/259366a57522459f96d0d859e4cd3dc925dd1abf/docs/help.md#llm-schemas-dsl---help