Support encoding short tensors into BGV ciphertexts of restricted dimension

OpenFHE's MakePackedPlaintext will zero-pad to the ring degree N, and this breaks the rotate-and-reduce trick, so instead in the simple_sum_test.cpp test harness, I manually repeat the coefficients cyclically until it fills the whole ciphertext. I'd like to add this to the compilation pipeline and the encode helper, and it suggests a bunch more work to do if we have an input cleartext tensor that is not divisible by the OpenFHE's ring degree (rotate-and-reduce tricks won't work in that case, or will have to be tweaked to account for the true underlying ring degree).

So this breaks down into two pieces:

- Support auto-generating the cyclic repetition code in the add-client-interface helper
- Determine how to handle inputs that are not divisible by the RLWE tensor size used by a backend (this dips into issues with parameter selection)