Rust threadsafety annotation changed in release 2.6.0

[aseyboldt]

In version 2.5.0 the StanLibrary struct was marked as Send and Sync:
https://docs.rs/bridgestan/2.5.0/bridgestan/struct.StanLibrary.html#synthetic-implementations
But in 2.6.0 the same struct is marked as not Send and Sync:
https://docs.rs/bridgestan/latest/bridgestan/struct.StanLibrary.html#synthetic-implementations

If some entry on the c-side changed from const to non-const, that might explain why this is suddenly different, but I couldn't find any such change.
So maybe the update of bindgen triggered this?

I think StanLibrary is in fact threadsafe, I can't see any reason why different threads couldn't create models at the same time? But maybe I'm missing something on the C++ side...

If we think it should be safe, I can make a simple PR that informs rust about this.

[WardBrian]

I'm re-opening this issue until we actually release the patch as a reminder to myself