Refactor `RustTarget` #2472

Job	Run time
msrv	51s
minimal	17s
docs	24s
rustfmt-clippy	29s
check-cfg	21s
quickchecking	19s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 41s
test-book	8s
test-expectations (ubuntu-latest)	51s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 39s
test-expectations (macos-12)	1m 0s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	1m 41s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 40s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	2m 8s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	2m 20s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 12s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 12s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	3m 59s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	3m 59s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	3m 56s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	4m 14s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	4m 49s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	4m 39s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	4m 51s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	5m 0s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 44s
test (macos-12, 9.0, 0, 0, 0)	2m 4s
success	1s
	59m 29s

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