Move result structures to a more appropriate location

rust/sea_battle_backend/src/utils/res_utils.rs

@@ -0,0 +1,9 @@
+use std::error::Error;
+use std::fmt::Display;
+use std::io::ErrorKind;
+
+pub type Res<E = ()> = Result<E, Box<dyn Error>>;
+
+pub fn boxed_error<D: Display>(msg: D) -> Box<dyn Error> {
+    Box::new(std::io::Error::new(ErrorKind::Other, msg.to_string()))
+}