Change `Callbacks` API. #1961

Job	Run time
minimal	20s
rustfmt-clippy	28s
check-cfg	20s
docs	23s
msrv	3m 59s
quickchecking	14s
test-book	7s
test-expectations (ubuntu-latest)	58s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	2m 29s
test-expectations (macos-latest)	1m 47s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 53s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	2m 12s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 59s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	3m 8s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	2m 28s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 22s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 19s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	2m 41s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	2m 39s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	2m 32s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	2m 35s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	3m 7s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	2m 59s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	3m 4s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	3m 0s
test (ubuntu-latest, 16.0, 0, 0, 1)	2m 15s
test (macos-latest, 9.0, 0, 0, 0)	2m 2s
success	1s
	54m 21s

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