chore(test): migrate unit tests from unittest to pytest nvidia test eval (#3249)

# What does this PR do?
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This PR migrates `unittest` to `pytest` in
`tests/unit/providers/nvidia/test_eval.py`.

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Part of #2680

Supersedes #2791

Signed-off-by: Mustafa Elbehery <[email protected]>

Author: Elbehery