fix: update versions and readme

[rohitpid]

Updated:

• gym 26.2
• gym-super-mario-bros 7.4.0
• code changes for new versions
• added poetry installation
• updated readme to reflect poetry instructions
• reduce memory footprint so to less than 8gb of VRAM so that OOM crashes for lower spec GPUs are prevented
• save checkpoints more often
• default to starting from checkpoint file in repo