Simplify how variants are handled #1823

Job	Run time
docs	2m 57s
clippy	1m 59s
nightly	3m 29s
msrv	1m 35s
rustfmt	12s
basics	1s
wasm	1m 12s
build_feature (alloc)	3m 22s
test_doc	6m 7s
build_feature (cli)	3m 49s
no_std (ubuntu-latest, minimal)	1m 5s
build_feature (cli,doc)	3m 52s
no_std (macos-latest, minimal)	1m 4s
build_feature (cli,fmt)	4m 18s
test_lib	2m 53s
build_feature (doc)	3m 45s
build_feature (workspace)	3m 28s
build_feature (languageserver)	3m 57s
test_miri (rune)	3m 21s
test_rune	2m 50s
build_feature (byte-code)	3m 24s
test_miri (rune-core)	45s
build_feature (capture-io)	3m 13s
test_miri (rune-alloc)	5m 57s
build_feature (emit)	3m 24s
	1h 11m 59s

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