script: add SCRIPT_ERR_SCRIPTNUM error

It will be used for errors related to CScriptNum (e.g. overflow or encoding errors).
Currently, we simply return unknown error for these errors.

src/script/script_error.cpp

@@ -117,6 +117,8 @@ std::string ScriptErrorString(const ScriptError serror)
             return "Using OP_CODESEPARATOR in non-witness script";
         case SCRIPT_ERR_SIG_FINDANDDELETE:
             return "Signature is found in scriptCode";
+        case SCRIPT_ERR_SCRIPTNUM:
+            return "Script number overflowed or is non-minimally encoded";
         case SCRIPT_ERR_UNKNOWN_ERROR:
         case SCRIPT_ERR_ERROR_COUNT:
         default: break;

src/script/script_error.h

@@ -14,6 +14,7 @@ typedef enum ScriptError_t
     SCRIPT_ERR_UNKNOWN_ERROR,
     SCRIPT_ERR_EVAL_FALSE,
     SCRIPT_ERR_OP_RETURN,
+    SCRIPT_ERR_SCRIPTNUM,
 
     /* Max sizes */
     SCRIPT_ERR_SCRIPT_SIZE,