Custom worker environment doesn't support extra libraries

**Describe the bug**

NemoRL allows to create custom environments and custom workers. If any additional package is needed in a custom environment, it's enough to use `py_executable` `uv run --with ` but with custom worker it doesn't work.

So far looks like /opt/venvs/... is created and then reused without considering "--with" package

**Steps/Code to reproduce bug**

TODO (for me): to create a reproducible setup for this bug as it may not be obvious what I mean by custom worker

**Expected behavior**

Either fix `uv run --with` or support `shell=True` in `subprocess.run` to have `py_executable` like `uv add && uv run`