der: add workspace-level `clippy` config #2355

Job	Run time
test (1.85.0)	31s
test (stable)	26s
build (stable, wasm32-unknown-unknown)	17s
build (1.85.0, wasm32-unknown-unknown)	21s
build (1.85.0, thumbv7em-none-eabi)	18s
build (stable, thumbv7em-none-eabi)	19s
minimal-versions / minimal-versions	27s
	2m 39s

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