Scheme Selection passes

I am currently working on a scheme selection process intended for non-expert users, enabling them to choose the most suitable FHE scheme for their task, i.e. their `mlir` file. The code is located at https://github.com/Fraunhofer-AISEC/heir/tree/scheme_selection. At present, I am annotating the `func` operation with counters for different types of computation, i.e. operations on reals, integers, etc. In a subsequent pass, I plan to use this information to select an appropriate FHE scheme for each `func` and annotate the `module` with the best scheme based on a majority vote.

I have the feeling that scheme selection is a slightly easier version of the scheme switching problem discussed in issue #300. The cost model needed for scheme selection is likely very similar to that required for scheme switching. I'd like to try to implement a more sophisticated cost model for the selection process, which could also be applied to scheme switching.

Any insights or feedback on this approach would be appreciated.