The subproject datastructures-immutable is based upon Google Guava

https://github.com/google/guava

License: Apache 2.0

as of 26 Dec 2023 (33.0.0) with thw following modifications:

- use only classes that are required for ImmutableCollection, ImmutableList, ImmutableSet, ImmutableEnumSet,
ImmutableMap, ImmutableBiMap, ImmutableEnumMap,

- javadocs cleaned up, no @since and no @author tags, no 'todos' to avoid confusion with the original project

- all annotations are removed (except @Override)

- all deprecations are removed

- all code relating to java serialization is removed

- all comments relating to Guava classes is renamed or removed

- all comments realting to GWT is removed

- all helper classes with static code (like Preconditions, Lists, Sets, Maps etc) are resolved and included into
existing classes, also from other Guava subpackages

- indentation level changed to 4

- lift Java language level to java 21

- use sealed classes for contractual integrity
