Simplify how variants are handled (#877) #1828

Job	Run time
docs	3m 7s
clippy	2m 4s
msrv	1m 29s
nightly	3m 18s
rustfmt	16s
basics	1s
build_feature (alloc)	3m 23s
no_std (ubuntu-latest, minimal)	1m 11s
build_feature (cli)	4m 5s
test_doc	6m 19s
no_std (macos-latest, minimal)	1m 16s
test_lib	4m 22s
build_feature (cli,doc)	3m 56s
build_feature (cli,fmt)	4m 0s
build_feature (doc)	3m 47s
test_miri (rune)	3m 31s
test_rune	2m 58s
build_feature (workspace)	3m 24s
wasm	1m 8s
test_miri (rune-core)	42s
build_feature (languageserver)	4m 22s
test_miri (rune-alloc)	5m 51s
build_feature (byte-code)	3m 23s
build_feature (capture-io)	3m 33s
build_feature (emit)	3m 45s
	1h 15m 11s

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