Support creating venvs from py_binarys

One of the features of aspect rules_py is that you can create a venv for any arbitrary py_binary / py_library. This is nice to have your 3rd party deps, along with potentially some first party deps in the venv. It would be pretty nice if this ruleset could do that as well, since switching to rules_py might be to heavy handed for some folks

Start by locating the rules_uv entry points for py_binary and py_library and any existing virtual-environment support. Compare how those targets expose dependencies, then define what creating a venv for arbitrary targets should accept and produce. Done means both py_binary and py_library targets can create usable virtual environments containing their third-party and applicable first-party dependencies.

Written by the indexing model from the issue text.