Support for cosmosage

[surak]

Why are these changes needed?

This pull request introduces support for the new cosmosage_v2 model into our system. The cosmosage_v2 model is a specialized language model designed for providing expert-level responses in the field of cosmology. The changes include

• documentation listing this model as supported
• conversation separator style
• conversation template
• model adapter

Related issue number (if applicable)

N/A

Checks

• [x] I've run format.sh to lint the changes in this PR.
• [x] I've included any doc changes needed.
• [x] I've made sure the relevant tests are passing (if applicable).

[surak]

@infwinston Would you care to have a look? I fear that this would start to diverge more and more from main as time passes.

[merrymercy]

@surak could you solve the conflicts?