Simplify how variants are handled #1825

Job	Run time
docs	2m 59s
clippy	2m 4s
nightly	3m 17s
msrv	1m 34s
rustfmt	13s
basics	1s
no_std (ubuntu-latest, minimal)	1m 7s
test_miri (rune)	3m 28s
no_std (macos-latest, minimal)	1m 3s
test_doc	6m 24s
test_miri (rune-core)	43s
test_miri (rune-alloc)	6m 0s
test_rune	2m 48s
test_lib	4m 9s
build_feature (alloc)	3m 29s
wasm	1m 13s
build_feature (cli)	4m 10s
build_feature (cli,doc)	4m 26s
build_feature (cli,fmt)	4m 0s
build_feature (doc)	3m 38s
build_feature (workspace)	3m 27s
build_feature (languageserver)	3m 46s
build_feature (byte-code)	3m 38s
build_feature (capture-io)	3m 28s
build_feature (emit)	3m 27s
	1h 14m 32s

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