cms

der: add `SetOfRef` struct #2964

Job	Run time
test (stable)	1m 37s
build (stable, wasm32-unknown-unknown)	49s
build (stable, thumbv7em-none-eabi)	32s
test (1.85.0)	1m 36s
build (1.85.0, thumbv7em-none-eabi)	33s
build (1.85.0, wasm32-unknown-unknown)	32s
minimal-versions	-1s
	5m 38s

Provide feedback