Fix disk space blowup by adding cache clean

[amrit110]

This pull request updates the Docker build and CI workflow to improve reliability and support development on the f/sglang-support branch. The most important changes include updating the workflow triggers, switching the runner environment for Docker builds, and optimizing cache management in the Dockerfile.

CI Workflow Improvements:

• Changed the Docker build job runner from self-hosted/docker to ubuntu-latest to improve consistency and reduce dependency on custom runners.

Dockerfile Optimization:

• Added the --no-cache option to the uv pip install command in Dockerfile and ensured removal of temporary cache directories to reduce image size and avoid stale package issues.