fix(client-java): repair illegal unicode escape in jsonString comment

The Client.Java-041 escaping fix left a literal \u00XX in a // comment; Java
processes \u unicode escapes even in comments, so it failed to compile on
windev (MxGatewayCli.java:2223 illegal unicode escape). Reworded the comment to
plain ASCII. The escaping code itself (String.format with the doubled-backslash
format string) was already correct.

clients/java/zb-mom-ww-mxgateway-cli/src/main/java/com/zb/mom/ww/mxgateway/cli/MxGatewayCli.java

@@ -2220,8 +2220,9 @@ public final class MxGatewayCli implements Callable<Integer> {
     // Package-private for the Client.Java-041 escaping regression test.
     static String jsonString(String value) {
         // RFC 8259 requires the two-character escapes for the named control
-        // characters and \u00XX escapes for the remaining U+0000–U+001F (and
-        // U+007F) range. The old implementation escaped only \\ \" \r \n, so a
+        // characters and six-character uXXXX escapes for the remaining
+        // U+0000-U+001F (and U+007F) range. The old implementation escaped only
+        // backslash, quote, CR, and LF, so a
         // value containing a tab, backspace, form-feed, or any other control
         // character produced malformed JSON (Client.Java-041).
         StringBuilder builder = new StringBuilder(value.length() + 2);