v0 mangling breaks hot-patching

Today's nightly (`nightly-2025-11-21`) has switched to v0 mangling by default, see [the announcement](https://blog.rust-lang.org/2025/11/20/switching-to-v0-mangling-on-nightly/).

I like getting in trouble so I switched to it today, and noticed that it breaks hot-patching because the wbindgen workaround you have relies on the the C++ like mangled form.

My proposed fix is to rely on the rustc-demangle crate instead.

I'm working on a PR, I'll submit it as soon as I can.

Also it might be time to poke the wbindgen folks about https://github.com/wasm-bindgen/wasm-bindgen/issues/4494