elliptic-curve: bump `crypto-bigint` to v0.7.0-rc.16 #3837

Job	Run time
test (1.85.0)	34s
test (nightly)	32s
test-miri	42s
build (1.85.0, wasm32-unknown-unknown)	41s
test (stable)	30s
build (stable, thumbv7em-none-eabi)	42s
build (1.85.0, thumbv7em-none-eabi)	44s
build (stable, wasm32-unknown-unknown)	36s
test-careful	1m 1s
minimal-versions	0s
	6m 2s

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