v0.6.0: make height_breach_penalty configurable per TetrisEnv instance

v0.5.1: re-enable decaying height breach penalty from line 4

v0.5.0: reduce game_over to -50, disable height breach penalty

chore: add version string to game_engine.py (0.4.0)

feat: decaying height breach penalty based on pieces placed

feat: add one-time height breach penalty (-50 per level above 4)

fix: reduce step penalty from -1 to -0.1

fix: remove height penalty, hole penalty only for new holes

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