elliptic-curve: add missing `Debug` impls (#1675) #2466

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	56s
test (1.65.0)	53s
test (stable)	10s
build (1.65.0, wasm32-unknown-unknown)	55s
build (stable, thumbv7em-none-eabi)	8s
build (stable, wasm32-unknown-unknown)	14s
	3m 16s

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