Fix examples CI without optional RLlib dependencies

[divyanshu-iitian]

Summary

• collect RLlib tests normally and skip them at class level when the optional Gymnasium/RLlib extras are unavailable
• defer optional imports until skipped tests actually run, avoiding collection failures
• scope lint and type-check import diagnostics in RLlib-only modules to their intentionally optional dependencies

This keeps the required examples workflow successful without making the large RLlib dependency set part of the core installation.

Fixes #316

Testing

• python -m pytest examples/rllib -q: 6 skipped, exit code 0
• pylint --errors-only examples/rllib: passed