Various fixes

[Hardcode3]

📌 Various fixes

📄 Description

• Added missing bitwise exclusive or ^ & ^= operators for Bitboard objects (+tests)
• generate_attacks now x-rays kings. It still does not x-ray other pieces. This change originates from a bug where the king could move away from the sliding piece checker. Now squares beyond the king are attacked and therefore are not available to move to.
• Removed check mask argument for king legal moves generation function. This changes originates from a bug where the check mask was applied to filter the king moves, therefore constraining the moves to the ray between the sliding attacker and the king, discarding relevant escape moves.
• Implemented a missing function (+tests) to determine real checkers based on board occupancy. The previous code introduced a bug since checkers was simply the intersection between the occupancy and the geometric attacks for a given square. Therefore it was finding much more checkers than possible.
• Updated legal moves generation function to support the changes made in this PR (+tests).
• Other print statements cleanup in the codebase

🧩 Type of Change

• 🐛 Bug fix
• ✨ New feature