Support for `hashbrown`

[rosingrind]

It will be great to have encoding support for https://crates.io/crates/hashbrown as it's generally better for data storage, and such storages often do serialize to and from binary data. As far as I know, there are only impls for serde now https://github.com/rust-lang/hashbrown/blob/v0.15.1/src/external_trait_impls/serde.rs

[finnbear]

Thanks for the issue! Our motivation to support this, like other crates, depends on how much demand there is.

For now, you can use the serde version of bitcode.