chore: share case swaping code

Author: Christopher-Chianelli

jpyinterpreter/src/main/java/ai/timefold/jpyinterpreter/types/PythonByteArray.java

@@ -1909,10 +1909,7 @@ public PythonByteArray swapCase() {
                     if (cp >= 128) {
                         return cp;
                     }
-                    if (Character.isLowerCase(cp)) {
-                        return Character.toUpperCase(cp);
-                    }
-                    return Character.toLowerCase(cp);
+                    return PythonString.CharacterCase.swapCase(cp);
                 }
         ).asAsciiByteArray();
     }

jpyinterpreter/src/main/java/ai/timefold/jpyinterpreter/types/PythonBytes.java

@@ -1681,10 +1681,7 @@ public PythonBytes swapCase() {
                     if (cp >= 128) {
                         return cp;
                     }
-                    if (Character.isLowerCase(cp)) {
-                        return Character.toUpperCase(cp);
-                    }
-                    return Character.toLowerCase(cp);
+                    return PythonString.CharacterCase.swapCase(cp);
                 }
         ).asAsciiBytes();
     }

jpyinterpreter/src/main/java/ai/timefold/jpyinterpreter/types/PythonString.java

@@ -1057,7 +1057,7 @@ public PythonBoolean isUpper() {
         }
     }
 
-    private enum CharacterCase {
+    enum CharacterCase {
         UNCASED,
         LOWER,
         UPPER;