Add `SpecialRustType::Bytes` to `RustType`

The current typeshare implementation doesn't support translation of `Vec<u8>` to a target language appropriate `bytes` type. For Go, typeshare would translate it to `[]int` when it should be `[]byte` etc. We should add a new `SpecialRustType::Bytes` to `RustType` to allow us to correctly translate to `bytes` in each target language.