Add automatic read/write items for all pocket items (1-40) (#51)

Decentralizes pocket injection logic from SysBotUI so that other auto-injectors can be passed in (future? like terrain/overworld items).

Adds validation to not modify items if the pocket data doesn't have the expected layout.

Closes #47 by implementing things in a more abstract & extendable way. Thanks @jfmherokiller for the example implementation which served as an inspiration!

NHSE.Injection/SysBot/Decoder.cs

@@ -0,0 +1,51 @@
+using System;
+
+namespace NHSE.Injection
+{
+    public static class Decoder
+    {
+        private static bool IsNum(char c) => (uint)(c - '0') <= 9;
+        private static bool IsHexUpper(char c) => (uint)(c - 'A') <= 5;
+
+        public static byte[] ConvertHexByteStringToBytes(byte[] bytes)
+        {
+            var dest = new byte[bytes.Length / 2];
+            for (int i = 0; i < dest.Length; i++)
+            {
+                int ofs = i * 2;
+                var _0 = (char)bytes[ofs + 0];
+                var _1 = (char)bytes[ofs + 1];
+                dest[i] = DecodeTuple(_0, _1);
+            }
+            return dest;
+        }
+
+        private static byte DecodeTuple(char _0, char _1)
+        {
+            byte result;
+            if (IsNum(_0))
+                result = (byte)((_0 - '0') << 4);
+            else if (IsHexUpper(_0))
+                result = (byte)((_0 - 'A' + 10) << 4);
+            else
+                throw new ArgumentOutOfRangeException(nameof(_0));
+
+            if (IsNum(_1))
+                result |= (byte)(_1 - '0');
+            else if (IsHexUpper(_1))
+                result |= (byte)(_1 - 'A' + 10);
+            else
+                throw new ArgumentOutOfRangeException(nameof(_1));
+            return result;
+        }
+
+        public static byte[] StringToByteArray(string hex)
+        {
+            int NumberChars = hex.Length;
+            byte[] bytes = new byte[NumberChars / 2];
+            for (int i = 0; i < NumberChars; i += 2)
+                bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
+            return bytes;
+        }
+    }
+}