Remove castling rights change check for half move increment

[farouk-chessly]

Current behaviour When checking if the half move clock should be incremented: If there is a change in castling rights then the half move clock is set back to 0.

Expected behaviour According to several sources, half move clock should not be set to 0 when castling rights change but incremented.

• Chess programming half move clock
• Chess programming castling
  • See section on irreversibility (used in detecting repetitions) however does not reset half move clock
• Also tested this out on Lichess and the half move clock is incremented when castling, see this study I made as an example. (To see FEN, go to share/export tab and scroll down).

Thanks for the awesome library!

[notnil]

Good catch. I agree with your interpretation. @farouk-chessly would you be willing to add a test specifically for this phenomenon? I will also have to double check repeatability with this issue in mind.

[notnil]

To edit the PR, it created a new one: #110

Thanks @farouk-chessly