Example fails on Lattigo branch

Example 3 fails on the lattigo branch. The problem is apparently related to the magnitude of the plaintext, (it can be fixed by setting `plaintext_inf_norm` to 2), but this isn't a problem with SEAL.

Start by reproducing Example 3 on the lattigo branch and compare its behavior with SEAL. Investigate how the plaintext magnitude and `plaintext_inf_norm` affect the failure, then review the closed merged pull request #164 for prior work. Done means Example 3 succeeds without an unintended workaround and the behavior is covered by an appropriate regression check.

Written by the indexing model from the issue text.