Add PairValidator class for custom validation of even integers

hibernate-project/src/main/java/com/humanbooster/annotation/PairValidator.java

@@ -0,0 +1,12 @@
+package com.humanbooster.annotation;
+
+import jakarta.validation.ConstraintValidator;
+import jakarta.validation.ConstraintValidatorContext;
+
+public class PairValidator implements ConstraintValidator<Pair, Integer> {
+
+    @Override
+    public boolean isValid(Integer integer, ConstraintValidatorContext constraintValidatorContext) {
+        return (integer != null) && (integer % 2 == 0);
+    }
+}