Ignore render_mode for CoGames MettaGrid env

[relh]

Summary

• Stop assigning render_mode in the CoGames env wrapper.
• Keep the render_mode argument for API compatibility.

Context

MettaGridPufferEnv exposes a read‑only render_mode that always reports "ansi". Assigning to it raises an AttributeError. The simplest fix is to accept render_mode in the wrapper but ignore it so CoGames training runs without error and behavior stays unchanged.

Testing

• python -m pufferlib.pufferl train cogames.cogs_v_clips.training_facility.harvest --train.total-timesteps 2000 --vec.num-envs 1 --vec.num-workers 1 --train.batch-size 64 --train.minibatch-size 64 --train.device cpu --env.render-mode none