build

Add `codecov` support to CI #131

Job	Run time
clippy	1m 5s
build (stable, --features "")	1m 23s
codecov	2s
fmt	19s
build (stable, --all-features)	1m 52s
build (stable, --no-default-features)	23s
build (1.71, --features "")	44s
test	2m 18s
build (1.71, --all-features)	1m 56s
build (1.71, --no-default-features)	38s
build (beta, --features "")	1m 4s
build (beta, --all-features)	2m 18s
build (beta, --no-default-features)	45s
build (nightly, --features "")	56s
build (nightly, --all-features)	1m 48s
build (nightly, --no-default-features)	40s
	18m 11s

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