der: add workspace-level `clippy` config (#2231) #2356

Job	Run time
test (stable)	30s
test (1.85.0)	27s
build (1.85.0, wasm32-unknown-unknown)	16s
build (stable, thumbv7em-none-eabi)	17s
build (stable, wasm32-unknown-unknown)	18s
minimal-versions / minimal-versions	32s
build (1.85.0, thumbv7em-none-eabi)	18s
	2m 38s

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