tests for lean_public are very slow

[Roland Haas]

Right now, out of the 10 slowest tests, 5 are lean_public and 1 is twopunctures_kerrproca_c11 . With 339 tests in the ET one tries to encourage each test to run as quickly as possible (https://docs.einsteintoolkit.org/et-docs/Adding_a_test_case).

With about 6 minutes runtime and about 25minutes total test runtime (https://einsteintoolkit.github.io/tests/plot.html in the time taken tab) this accounts for almost 1/4 of the test runtime (not including build time).