Add BitFlip environment

[davidhpark]

Add BitFlip Environment to PufferLib

BitFlip is a simple 1D game where the goal is to match the current state to a target pattern by flipping the necessary bits.

In this PufferLib variant:

• Top row: target pattern
• Middle row: current state
• Bottom row: cursor position

Available actions:

• Left — move cursor left
• Right — move cursor right
• Up — flip the bit at the cursor