Ideas for swc_alloactor

[kdy1]

Tasks

Beta Give feedback

1. (Maybe) Change Allocator.scope to an unsafe function. (refactor(allocator): Use RAII guard instead of scope #9254)
2. Transmute at https://github.com/swc-project/swc/blob/d2e96bf40f6cfe60b7b1d7ef3b77efacebaad675/crates/swc_allocator/src/alloc.rs#L36-L39 is not safe
3. Run miri
4. Assertions to check escape from arenas (We need both of feature = "debug" and cfg!(debug_assertions)).
5. Change scope API to RAII (refactor(allocator): Use RAII guard instead of scope #9254)
6. It should optimize only on nightly and just act as std types on stable rustc. We need #[fundamental] to behave correctly. feat(allocator): Feature gate nightly via macros #9274
7. refactor(visit): Pre-generate visitor code #9262
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