Add option to generate safe and unsafe conversions for rustified enums #2709

Job	Run time
docs	19s
check-cfg	26s
minimal	14s
msrv	53s
quickchecking	26s
rustfmt-clippy	27s
test-book	12s
test (ubuntu-latest, 9.0, 0, 0, 0, 0)	1m 26s
test (ubuntu-latest, 9.0, 0, 0, 1, 0)	1m 24s
test-expectations (ubuntu-latest)	40s
test-no-headers	28s
test (ubuntu-latest, 9.0, 0, 1, 0, 0)	1m 38s
test-expectations (macos-latest)	51s
test (ubuntu-latest, 9.0, 0, 1, 1, 0)	1m 25s
test (ubuntu-latest, 9.0, 1, 0, 0, 0)	1m 39s
test (ubuntu-latest, 9.0, 1, 0, 1, 0)	1m 39s
test (ubuntu-latest, 9.0, 1, 1, 0, 0)	1m 39s
test (ubuntu-latest, 9.0, 1, 1, 1, 0)	1m 38s
test (ubuntu-latest, 16.0, 0, 0, 0, 0)	1m 40s
test (ubuntu-latest, 16.0, 0, 0, 1, 0)	1m 39s
test (ubuntu-latest, 16.0, 0, 1, 0, 0)	1m 39s
test (ubuntu-latest, 16.0, 0, 1, 1, 0)	1m 38s
test (ubuntu-latest, 16.0, 1, 0, 0, 0)	1m 26s
test (ubuntu-latest, 16.0, 1, 0, 1, 0)	1m 26s
test (ubuntu-latest, 16.0, 1, 1, 0, 0)	1m 38s
test (ubuntu-latest, 16.0, 1, 1, 1, 0)	1m 38s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 38s
test (macos-latest, 16.0, 0, 0, 0)	1m 41s
success	1s
	33m 28s

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