rune: Store Generator and Stream in AnyObj instead of Mutable (relate… #1785

Job	Run time
docs	3m 23s
clippy	2m 4s
msrv	1m 30s
nightly	3m 5s
rustfmt	13s
basics	1s
no_std (ubuntu-latest, minimal)	1m 3s
test_miri (rune, runtime:: hir::arena:: --skip runtime::vm:: --skip runtime::vm_execution:: )	2m 28s
no_std (macos-latest, minimal)	1m 4s
test_doc	6m 6s
test_miri (rune-alloc)	6m 5s
build_feature (alloc)	3m 26s
test_lib	4m 8s
build_feature (cli)	4m 0s
test_rune	2m 48s
wasm	1m 16s
build_feature (cli,doc)	4m 2s
build_feature (cli,fmt)	3m 58s
build_feature (doc)	3m 43s
build_feature (workspace)	3m 19s
build_feature (languageserver)	3m 53s
build_feature (byte-code)	3m 27s
build_feature (capture-io)	3m 41s
build_feature (emit)	3m 30s
	1h 12m 13s

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