ed448

rfc6979: integrate with `crypto-bigint`; `KGenerator` API #1213

Job	Run time
test (stable)	11s
build (thumbv7em-none-eabi, stable)	19s
build (wasm32-unknown-unknown, 1.85.0)	19s
build (thumbv7em-none-eabi, 1.85.0)	17s
build (wasm32-unknown-unknown, stable)	17s
test (1.85.0)	17s
	1m 40s

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