[Test] Generate Franka Pour resets for contrib smoke test

[maxkra15]

Summary

• Generate the smallest valid Franka Pour reset dataset on demand for its contributed-environment smoke case.
• Reuse the shipped generator and its default artifact path, and skip generation when an artifact already exists.
• Keep the task, generator defaults, and all user-facing runtime behavior unchanged.

Root cause

isaac-sim#7068 removes the former explicit Franka Pour skip and exercises the task from a clean checkout, where the intentionally ignored reset artifact is absent. The environment therefore raises FileNotFoundError before the random-action smoke rollout begins.

This PR is stacked directly on the head of isaac-sim#7068 so it contains only the focused test fix.

Validation

• Started without datasets/franka_pour/reset_dataset.pt.
• Ran test_contrib_environments[IsaacContrib-Franka-Pour-2-cuda] directly.
• Result: 1 passed, 304 deselected in 41.44 seconds.
• The test generated a validated 106-row, 42,245-byte artifact and then successfully created and stepped the Pour environment.
• Ruff, Ruff format, whitespace, spelling, license, YAML/TOML, conflict, private-key, debug-statement, and Git LFS hooks passed. The full changelog hook remains blocked by pre-existing divergence in the stacked base branch.