[rezataroosheh]

What

Adds tests for EnumSet fields in MessageProcessorTest:

• testCustomMapperEnumSetMessage: an EnumSet field annotated with @CustomMapper, both on its own and nested in a collection. The generated serializer uses the custom mapper and creates an EnumSet on read.
• testEnumMapperCannotBeTwoEnumSets: a field that contains EnumSets of different enum types (Map<EnumSet<A>, EnumSet<B>>) fails code generation with the "Multiple enums of different types" error.

Only tests and test resources are changed.

Why

EnumSet support was added in IGNITE-28963, but tests didn't cover these two cases.

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