Implementing unwind safety

We recently added support for building with `panic=unwind` in upstream Wasm Bindgen 0.2.107 in https://github.com/wasm-bindgen/wasm-bindgen/pull/4796. Wasm Stream has various usage cases that aren't unwind safe, which should be possible to fix to ensure support for building with unwind safety. We are using this crate in Cloudflare Rust Workers, so we could post a PR to add these fixes if there is availability for reviewing them. Would be great to confirm this is the right approach before we post the PR though.