Allow usage of 0x models in Copilot CLI

[vivganes]

Describe the feature or problem you'd like to solve

At the moment, I can only use models with a multiplier 1x (meaning there is a limit on usage) in copilot cli. This restricts a person who prefers GPT-4.1 (a 0x model) from trying the copilot

Proposed solution

Allow all models that are shown in Github Copilot VS Code extension.

Example prompts or workflows

No response

Additional context

No response

[RyanHecht]

Hi! We've gotten many requests for access to smaller models! We're tracking that ask in this issue: #32 -- leave a thumbs up over there!