DRAFT fix: prefer real NeMo-Gym package in actor

[snowmanwwg]

The PR fixes the old NeMo-Gym PARENT_DIR crash in NeMo-RL.

When NeMo-RL starts a NeMo-Gym actor, Python could accidentally grab the wrong folder named nemo_gym:

• Wrong one: examples/nemo_gym
• Correct one: 3rdparty/Gym-workspace/Gym/nemo_gym

The wrong one is just an examples folder, so it does not contain PARENT_DIR. That caused:

ImportError: cannot import name 'PARENT_DIR' from 'nemo_gym'

The PR makes NeMo-RL do this before starting NeMo-Gym:

1. Put the real NeMo-Gym package path first.
2. If Python already loaded the wrong examples/nemo_gym, clear it out.
3. Then import NeMo-Gym normally.

It also fixes a smaller environment bug: NeMo-RL was setting VIRTUAL_ENV to the Python executable path like:

.../bin/python

but it should point to the venv folder:

.../

So the PR makes that correct too.

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