rune: Remove Mutable::Result and Mutable::Option (#876) #1818

Job	Run time
clippy	2m 4s
docs	3m 29s
rustfmt	13s
msrv	1m 27s
nightly	5m 0s
basics	1s
wasm	1m 6s
no_std (ubuntu-latest, minimal)	1m 20s
no_std (macos-latest, minimal)	1m 24s
test_doc	6m 33s
build_feature (alloc)	3m 18s
test_lib	4m 10s
build_feature (cli)	3m 58s
build_feature (cli,doc)	3m 51s
test_rune	2m 53s
test_miri (rune)	3m 32s
build_feature (cli,fmt)	3m 54s
test_miri (rune-core)	59s
build_feature (doc)	3m 49s
test_miri (rune-alloc)	6m 5s
build_feature (workspace)	3m 36s
build_feature (languageserver)	3m 48s
build_feature (byte-code)	3m 24s
build_feature (capture-io)	3m 28s
build_feature (emit)	3m 18s
	1h 16m 40s

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