Fixed infinite size directly follows mappers

src/main/java/beamline/events/BEvent.java

src/main/java/beamline/mappers/DirectlyFollowsRelation.java

.../models/algorithms/InfiniteSizeDirectlyFollowsMapper.java

...va/beamline/models/responses/DirectlyFollowsRelation.java

src/main/java/beamline/sources/MQTTXesSource.java

src/test/java/beamline/tests/MapperTest.java

src/test/java/beamline/tests/SourcesTest.java

src/test/java/beamline/tests/Utils.java