Use Colab as a base image.

This change makes a number of major changes:
- Colab is the base image
- uv is the main package install tool
- leveraging requirements.txt instead of many separate installs
- stop building and installing tensorflow/torch/lightbgm/jax since those
  are managed by the Colab base image now

In order to decide what packages to explicitly install I:
- looked at what packages are in the Colab base image
- looked at what packages were in the Kaggle image
- looked at what packages were explicitly mentioned in Kaggle Dockerfile

This may still take a few iterations to get all the right parts in the
image, but this should hopefully make the image much more manageable.

http://b/365782129