Merge riir branch

[fenhl]

The riir branch, which is a translation of the service into Rust, has been running in production for over 2 years now (since the start of Zucchini), so it should really be merged into the default branch (which should also be renamed from master to main at that point). Some things that need to be done first:

• The Python module is still being used as a library from other Python code. Need to write a PyO3 interface to the new implementation.
• There are still some features missing from the rewrite. Need to check which features those are and port them.