Support Tuple observations in GymEnvironment

[mneetika]

Summary:

• Add support for Gym/Gymnasium Tuple observation spaces in GymEnvironment
• Flatten tuple observations from reset() and step() into 1-D tensors
• Convert tuple observation spaces into flattened BoxSpace bounds
• Keep Tuple action spaces unsupported

This addresses the Tuple observation-space case from #54, including environments such as Blackjack-v1.

Test Plan:

• python -m unittest test.unit.test_gym_environment
• python -m unittest test.unit.test_flatten_dict_observations
• python -m unittest test.unit.test_tutorials.test_frozen_lake

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