Add BuildCommand support and missing fields to API v3 Build endpoint
- Add BuildCommandSerializer for build command results
- Add commands field to BuildSerializer
- Add docs_url field to BuildSerializer
- Add commit_url field to BuildSerializer
- Add builder field to BuildSerializer
- Enable ?expand=notifications for Build endpoint
- Add comprehensive tests for new fields and expand functionality
- Update test fixtures to include new fields
Co-authored-by: ericholscher <25510+ericholscher@users.noreply.github.com>