feat(build): special handling for backends tracing output

[remimimimimi]

Description

Parse and format OTLP JSON traces from the backend. This allows to unconditionally print warnings and errors from the backend and conditionally output other traces on verbose mode.

Depends on prefix-dev/pixi-build-backends#463

How Has This Been Tested?

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: {e.g., Claude, Codex, GitHub Copilot, ChatGPT, etc.}

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.
• I have verified that changes that would impact the JSON schema have been made in schema/model.py.