`uv run` tries executing script if installed

[2022tgoel]

Summary

This PR implements a solution to https://github.com/astral-sh/uv/issues/9167. It prioritizes executing the uv run command as a python script, if the script is installed, over executing the command as a python package or external command.

Test Plan

I tested my solution against the repoduction of the issue created here: https://github.com/raqbit/uv-scripts-repro/, and verified that uv run foo now executes the python script.