applies chatgpt suggestions.

...
does not appear to decode everything

core/src/instruction2/from_bytes.rs

@@ -0,0 +1,23 @@
+use log::debug;
+use crate::address_mode::AddressMode::*;
+use crate::constants::constants_isa_op::*;
+
+fn join_word(low: u8, high: u8) -> u16 {
+    ((high as u16) << 8) | low as u16
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_join_word() {
+        let low: u8 = 0xcd;
+        let high: u8 = 0xab;
+
+        assert_eq!(
+            join_word(low, high),
+            0xabcd
+        );
+    }
+}