v0.12.0

• Fix Game::play not resetting passed_last_turn!
• Add missing benchmark description to benches/README.md
• Remove deprecated authors field in Cargo.toml
• Add explicit feature flags instead of relying on implicit behavior
• Update dependencies
• Improve serde example
• Fix ShadowBoard::arbitrary never generating bit 63
• Fix swapped benchmark names for bits/hot_bits extraction
• Replace "undefined behavior" wording with "incorrect board state"
• Implement Display and Error for OthelloError and PositionError
• Revised derives for various structs and enums.
• Change Stone::flip to take self by value
• Make count_set and count_empty use consistent conversion approach
• Updated CI workflows
• Split OthelloError into two distinct error types
• Expanded PositionError to include more specific error conditions
• Update README and documentation in lib.rs