Render Rust API docs

[fsimonis]

We can use cargo rustdoc to build a stand-alone documentation that can be integrated into the website similar to doxygen.

We cannot use the doc.rs project to autobuild the documentation as they use Ubuntu 24.04 and preCICE needed to be available in the Ubuntu archives.

https://github.com/rust-lang/crates-build-env?tab=readme-ov-file#adding-new-dependencies

[fsimonis]

Turns out that we can use docs.rs by not building the native part when DOCS_RS is detected.
I released a hotfix version that now builds successfully on docs.rs:

https://docs.rs/precice/latest/precice/struct.Participant.html