bug: document formatting when using Anthropic

[milancermak]

• I have looked for existing issues (including closed) about this

Bug Report

Anthropic expects documents to be structured in a particular XML format. This is currently not the case - the documents are wrapped in <attachments> tags.

Expected behavior

When using an Anthropic model, I expect the request from Rig to be formatted correctly according to what the Anthropic API expects and recommends.

Additional context

The issue might be resolved once #149 is addressed.

[0xMochan]

Thanks for this issue, 100% this seems like the correct approach. The XML format chosen in the codebase currently was chosen a bit arbitrarily. It's likely that this isn't an enforced format but it's definitely a change we should make standardized.

I think this is a great first issue and either could be adapted globally OR just specifically for anthropic.