der: add const ::new to Length, BytesRef, AnyRef (#1713) #2323

Job	Run time
build (stable, thumbv7em-none-eabi)	44s
fuzz	2m 9s
build (1.81.0, thumbv7em-none-eabi)	51s
test (stable)	2m 20s
test (1.81.0)	2m 33s
build (stable, wasm32-unknown-unknown)	51s
build (1.81.0, wasm32-unknown-unknown)	55s
minimal-versions	0s
	10m 23s

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