disable doctest from erronious comment parsing

Currently, at least on my machine, pipewire-rs does not pass tests when running cargo test due to the docstrings attached to pw_time. Markdown syntax defines code blocks as any line starting with at least 4 spaces, and as such tries to interpret the graphs drawn in the comments as code.

This is an issue with how rust-bindgen reads in comments, see https://github.com/rust-lang/rust-bindgen/issues/1313

The current solution, particularly as I assume pipewire-sys wouldn't have doctests in general is to simply disable doctests in the generated bindings.

Edit: pipewire-rs -> pipewire-sys