docs: enable nightly-only docsrs (#76) #602

Job	Run time
Build & test (stable, ubuntu-latest)	1m 55s
Build & test (stable, macos-latest)	1m 24s
Build & test (stable, windows-latest)	4m 10s
Build & test (nightly, ubuntu-latest)	3m 59s
Build & test (nightly, macos-latest)	4m 54s
Build & test (nightly, windows-latest)	8m 12s
Test coverage checks	3m 59s
Clippy lint checks	44s
Machete dependencies checks	11s
Test with external dependencies	4m 19s
Minimal dependency versions build	1m 18s
Code formatting checks	18s
	35m 23s

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