fix(go/ai): error if multiple tool requests share Ref

[kwjw]

Resolves #2224.

If the same tool is called multiple times in the same request, then the tool requests must have distinct Ref values.

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)

[apascal07]

This is one way to solve this but any model-generated refs aren't significant, we can just fill them in ourselves with an index or similar if they're not filled in by the model.

[pavelgj]

This is one way to solve this but any model-generated refs aren't significant, we can just fill them in ourselves with an index or similar if they're not filled in by the model.

Can use #2250 for reference