test: fix contributing test setup

[han-xudong]

Summary

• add the missing dev extra required by uv run --extra dev pytest -n 4
• skip optional policy backends when their large runtime dependencies are not installed
• fix policy interface test configuration and middleware kwargs passthrough
• isolate middleware test ports so xdist workers do not collide
• resolve snake_case policy modules such as GearSonic / GearSonicPlanner

Issue

Fixes #4.

Validation

• uv run --extra dev pytest -n 4 -q
• uvx ruff check pyproject.toml rio/_tests/test_mw.py rio/_tests/test_policy.py rio/_tests/test_policy_node.py rio/_tests/test_safety.py rio/envs/factory.py rio/policies/policy_interface.py
• uvx ruff format --check pyproject.toml rio/_tests/test_mw.py rio/_tests/test_policy.py rio/_tests/test_policy_node.py rio/_tests/test_safety.py rio/envs/factory.py rio/policies/policy_interface.py
• uvx typos --diff pyproject.toml rio/_tests/test_mw.py rio/_tests/test_policy.py rio/_tests/test_policy_node.py rio/_tests/test_safety.py rio/envs/factory.py rio/policies/policy_interface.py

Notes

This keeps optional VLA / humanoid policy tests collected, but skips them when their documented optional dependencies are absent.

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