Lint Rust demos with clippy

[Hofer-Julian]

One thing that would be good to have is to check all Rust demos with clippy.
Clippy both ensures that they build correctly, but also acts as a linter.
Looking at the code it seems like we currently lint with language servers.
That is possible with rust-analyzer, but it's also wasteful compared to just running cargo clippy directly.

What I think should be done:

• Loop through each demo
• Copy all relevant Rust files into the demo
• Run cargo clippy (make sure that target dir is set correctly)
• Remove copied Rust files again

[sonnyp]

The reason we use the LSP to lint is to guarantee 100% compat with Workbench.

It prevents shipping demos that have errors or warnings once users open them in Workbench.
Think of it as headless Workbench.

Eventually we might even open a full Workbench session for each single demo anyway in order to do UI automation tests and screenshot tests.