der

der: add `SetOfRef` struct #4484

Job	Run time
test-derive (1.85.0)	32s
test-careful	1m 24s
test-cross (powerpc-unknown-linux-gnu)	2m 8s
test-derive (stable)	30s
test-heapless	36s
build-no-std	2m 35s
test-cross (armv7-unknown-linux-gnueabi)	2m 5s
test-wasm	55s
test-miri (x86_64-unknown-linux-gnu)	54s
test-miri (s390x-unknown-linux-gnu)	1m 14s
minimal-versions / minimal-versions	2m 47s
test (x86_64-pc-windows-msvc, 1.85.0, windows-latest)	17m 0s
test (i686-unknown-linux-gnu, 1.85.0, sudo apt update && sudo apt install gcc-multilib)	7m 55s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	7m 34s
test (x86_64-unknown-linux-gnu, 1.85.0)	8m 56s
test (aarch64-unknown-linux-gnu, stable, ubuntu-24.04-arm)	6m 54s
test (aarch64-apple-darwin, 1.85.0, macos-latest)	11m 3s
test (aarch64-apple-darwin, stable, macos-latest)	9m 21s
test (x86_64-unknown-linux-gnu, stable)	7m 10s
test (aarch64-unknown-linux-gnu, 1.85.0, ubuntu-24.04-arm)	9m 29s
test (x86_64-pc-windows-msvc, stable, windows-latest)	15m 37s
	1h 56m 39s

Provide feedback