fails to compile without runtime

[dvc94ch]

Describe the bug

makes sense to reexport some of the types to a frontend, not clear why a runtime is required

To Reproduce

cargo build --no-default-features

Expected behavior

builds fine

Code snippets

No response

OS

any

Rust version

any

Library version

since build.rs was added 7mo ago

API version

not stripe related

Additional context

No response

[arlyon]

The library is not designed to just expose the types but I am open to a change that adapts it to do so, as there is nothing that inherently prevents it.