Refactor the `features` module #1652

Job	Run time
msrv	2m 5s
docs	36s
quickchecking	32s
minimal	15s
rustfmt-clippy	46s
test-expectations (ubuntu-latest)	1m 37s
test-expectations (macos-latest)	4m 11s
check-cfg	31s
test-book	12s
test (ubuntu-latest, 5.0, 1, 0, 0, 0, 0)	2m 40s
test (ubuntu-latest, 5.0, 1, 0, 0, 1, 0)	3m 10s
test (ubuntu-latest, 5.0, 1, 0, 1, 0, 0)	3m 15s
test (ubuntu-latest, 5.0, 1, 0, 1, 1, 0)	2m 39s
test (ubuntu-latest, 5.0, 1, 1, 0, 0, 0)	4m 0s
test (ubuntu-latest, 5.0, 1, 1, 0, 1, 0)	4m 19s
test (ubuntu-latest, 5.0, 1, 1, 1, 0, 0)	3m 42s
test (ubuntu-latest, 5.0, 1, 1, 1, 1, 0)	3m 35s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	2m 57s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	3m 3s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	3m 12s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	3m 6s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	5m 47s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	5m 49s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	4m 6s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	3m 40s
test (ubuntu-latest, 9.0, 0, 0, 1)	2m 6s
test (macos-latest, 9.0, 0, 0, 0)	2m 12s
	1h 14m 3s

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