feat(go): Added /util/generate + filled feature gaps in Generate API.

[apascal07]

A lot of things happening here because there was a lot busted while trying to add GenerateAction and make the parity tests pass:

• Updated Go schema from JS schema.
• Updated parts to support the correct tool request/response schemas.
• Updated model.Generate() to execute multiple + parallel tool requests.
• Added support for interrupts in tools (didn't need to be here but... it made it easier to consider the handleToolRequests() refactor).
• Added GenerateAction under /util/generate.
• Loosened the restrictions on tool schemas (can be anything now, including any, instead of map[string]any).
• Added APIs to control features like max turns, return tool requests, and tool choice (currently unused, plugins need to be updated).

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)