Improve debug str generator #2604

Job	Run time
docs	24s
minimal	19s
rustfmt-clippy	28s
msrv	49s
quickchecking	22s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 44s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 43s
test-expectations (ubuntu-latest)	50s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	1m 46s
check-cfg	21s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 46s
test-expectations (macos-12)	1m 13s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	2m 14s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	2m 18s
test-book	6s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 12s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 23s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	3m 57s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	3m 58s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	4m 3s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	4m 12s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	4m 52s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	4m 52s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	4m 41s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	4m 53s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 46s
test (macos-12, 9.0, 0, 0, 0)	1m 33s
success	1s
	59m 46s

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