This adds a new option (ignoringNonExistentFields) to recursive comparison that allows polymorphic objects with different field structures to be compared effectively. When enabled, the comparison will skip field existence validation, which is useful when comparing objects of different subtypes where some fields might only exist in certain implementations.

Overview

This PR adds a new feature to the recursive comparison functionality that allows ignoring non-existent field checks. This is particularly useful when comparing polymorphic objects where some fields might not exist in all subtypes.

Implementation Details

• Added ignoreNonExistentFields boolean flag to RecursiveComparisonConfiguration
• Added ignoringNonExistentFields() method to RecursiveComparisonAssert
• Added appropriate builder methods and setters
• Added early return in checkComparedFieldsExist when this option is enabled
• Added corresponding toString/description methods to show when this option is active
• Added unit tests to verify the behavior

Example Use Case

When comparing objects like:

class BaseClass {
    String commonField = "common";
}

class SubClass1 extends BaseClass {
    String subField1 = "sub1";
}

class SubClass2 extends BaseClass {
    // 'subField1' doesn't exist here
    String subField2 = "sub2";
}

Regular recursive comparison would fail due to field existence checks. With this new option:

SubClass1 actual = new SubClass1();
SubClass2 expected = new SubClass2();

// This will now pass
assertThat(actual)
    .usingRecursiveComparison()
    .ignoringNonExistentFields()
    .isEqualTo(expected);

Check List:

• Fixes Allow to ignore check on compared fields in the recursive comparison (initial issue description was: Problems on method 'usingRecursiveFieldByFieldElementComparatorOnFields') #3806
• Unit tests : YES
• Javadoc with a code example (on API only) : YES
• PR meets the contributing guidelines : YES