[explorer, moves, core] Improve error handling in explorer

Implement thiserror::Error for a bunch of error types, and remove string errors
from the implementation of the command handler in explorer.

Clean up parsing of basic types all over the place.

Update Cargo files to include thiserror and anyhow.

moves/src/builder.rs

@@ -4,15 +4,20 @@ use crate::{defs::Kind, Move, PromotionShape};
 use chessfriend_board::{castle, en_passant::EnPassant};
 use chessfriend_core::{Color, File, PlacedPiece, Rank, Square};
 use std::result::Result as StdResult;
+use thiserror::Error;
 
 pub type Result = std::result::Result<Move, Error>;
 type EncodedMoveResult = std::result::Result<u16, Error>;
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Error, Eq, PartialEq)]
 pub enum Error {
+    #[error("no origin square")]
     MissingOriginSquare,
+    #[error("no target square")]
     MissingTargetSquare,
+    #[error("no capture square")]
     MissingCaptureSquare,
+    #[error("invalid en passant square")]
     InvalidEnPassantSquare,
 }