Merged PR 248: Make observation flattening optional for agents.

## Summary
Same as other PR but this time we are merging into DEV.

The Proxy agent has a new config option, `flatten_obs`. If true, we use gymnasium flatten.

## Test process
Unit tests and inspection.

Related work items: #2143, #2154, #2161

src/primaite/game/game.py

@@ -432,6 +432,7 @@ class PrimaiteGame:
                     action_space=action_space,
                     observation_space=obs_space,
                     reward_function=rew_function,
+                    agent_settings=agent_settings,
                 )
                 game.agents.append(new_agent)
                 game.rl_agents.append(new_agent)