Add uv pip list --format json

[Daverball]

This is very helpful for interpreting the output of pip list in e.g. shell scripts using jq and then further process it to generate follow-up commands.

This in combination with #2150 is the last remaining blocker for me to be able to replace pip with uv in one of my projects (this also happens to be where I'm experiencing the most slowdowns).

[T-256]

Already working on it: #1998

[charliermarsh]

This was added in #1998.