Need reproducibility checks for higher order elements

We're currently checking that all elements can reproduce affine functions (i.e., patch tests). We should go further and verify that higher-order elements can reproduce polynomial solutions up to their order.

Locate the existing affine-function patch tests and run them to understand the current reproducibility coverage. Extend the checks for higher-order elements so each reproduces polynomial solutions through its order, then verify the expanded test suite passes.

Written by the indexing model from the issue text.