Simplify how variants are handled #1827

Job	Run time
msrv	1m 30s
nightly	3m 27s
docs	3m 19s
clippy	2m 8s
rustfmt	21s
basics	1s
no_std (ubuntu-latest, minimal)	1m 8s
wasm	1m 11s
no_std (macos-latest, minimal)	1m 6s
test_doc	6m 7s
build_feature (alloc)	3m 37s
test_lib	4m 3s
build_feature (cli)	3m 50s
test_miri (rune)	3m 43s
test_rune	2m 56s
build_feature (cli,doc)	3m 59s
test_miri (rune-core)	43s
build_feature (cli,fmt)	3m 59s
test_miri (rune-alloc)	5m 59s
build_feature (doc)	3m 45s
build_feature (workspace)	3m 18s
build_feature (languageserver)	4m 6s
build_feature (byte-code)	3m 21s
build_feature (capture-io)	3m 16s
build_feature (emit)	3m 27s
	1h 14m 20s

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