[Set] Use map[interface{}]struct{} to save some amount of memory
[Set] Use map[interface{}]struct{} to save some amount of memory

as struct{} needs 0 memory.

Signed-off-by: Anton Tiurin <b91bf98aa7cea39040737992640d61c368ae17fe@yandex.ru>

Workiva/go-datastructures,jlhonora/go-datastructures,golang-collections/go-datastructures,legendtkl/go-datastructures,Lanzafame/go-datastructures,brianshannan-wf/go-datastructures,evanh/go-datastructures,sdboyer/go-datastructures,tylertreat/go-datastructures,jim-slattery-rs/go-datastructures,tylertreat/go-datastructures,liufuqiang/go-datastructures,Workiva/go-datastructures,tomdeering-wf/go-datastructures,legendtkl/go-datastructures,legendtkl/go-datastructures,lsxia/go-datastructures,Charlesdong/go-datastructures,samklr-ds/go-datastructures,legendtkl/go-datastructures