Crystal Durham

If it wouldn't parse successfully otherwise, it's not breaking, as it's solely extending the allowed grammar. I don't believe there's any case where `//` is valid currently, where it would...

The use of symlinks in the linked repo might also be relevant.

Ok... I've just regenerated bindings with rust-bindgen 0.60.1 (previously 0.59.2), and found something interesting: `bindgen fmod_studio.h --blocklist-file ./fmod_common.h` blocklists the items from `fmod_common.h` but uses `__BindgenUnionField`. `bindgen fmod_studio.h --blocklist-file fmod_common.h`...

With modern Rust at least you can make a `union` of any type if you wrap it in `ManuallyDrop`, so perhaps that's just a missing feature (wrap unknown `Copy` types...

`extern "system"` is also useful.

https://github.com/tokio-rs/tracing/pull/2048 is related, since it makes more things able to be dynamically imported. The biggest hurdle AIUI for ingesting log's kvs into tracing is that tracing requires static `FieldSet` information....

Technically closes #372, though supplying a dynamic level still isn't advised per the added documentation.

(Sorry for flooding the actions queue with the rebase, but for this large PR I feel showing/proving each commit independently passes CI is important)

I think it should be possible to use [`sharded_slab::Pool`](https://docs.rs/sharded-slab/latest/sharded_slab/struct.Pool.html) to store the extensions as well as the always-present data, and to do so in a backwards-compatible manner. The backwards-compatible scheme...

I'd be happy to take a stab at it if you can find your old diff (and maybe even if you can't)