Implement AI targets

[kreibaum]

Maybe helps with training

Julia:

• Next Action / next action square conditioned on legal actions
• Legal Actions
• End of move square. I.e. pair move target or chain end
• Bitmap of all squares involved in the move/chain.
• Remaining chain duration

Rust:

• Threatened squares (mine, partner) - Done in 20b9f3fa807a2be03c58b2c8ee7f6094791bbad0
• Blocked pawns (mine, partner) - Done in 374cb80d936958764e15bcc878ac056d133f4dab
• Chain aligned pieces e.g. Knights who see each other? How exactly is that defined? - Won't do this without clear understanding what that is.