Allow extending LC merkle proof tests

[etan-status]

Currently, test_single_merkle_proof only supports BeaconState tests. For future tests, different object classes are desirable. Update format to allow testing other objects as well.

[ralexstokes]

what types of tests do you have in mind?

this approach isn't impossible but in general we would handle this kind of thing by making a new type of test "handler" that has the exact format we want -- that way consumers of the test data have less dynamism at runtime, which is desirable for all of the compiled language targets that consume these tests

[etan-status]

Using a different subfolder for each type is indeed cleaner, and more in line with e.g., ssz_static tests.
Changed it to use separate suite for now (within the single_merkle_proof handler, within the light_client runner).

As for future tests, I'd like to add one for BeaconBlockBody as well.

[dapplion]

LGTM

[hwwhww]

lgtm 👍

If we want to extend the coverage of Merkle proof tests, we can consider reworking the test generator main.py to something similar to ssz_static rather than using pytest + @spec_state_test. @etan-status Do you think that would be helpful?

[etan-status]

Currently, the idea for the LC merkle proof tests is to test for very specific cases (the 3-4 generalized indices necessary for the LC sync protocol) to also allow testing concrete implementations that only support what is actually needed over a generalized SSZ library. So, the tests are much more manual than something that can be generated dynamically.

The other difference is that the LC tests are all generated as part of make gen_light_client, so the output is one folder deeper as it's not a separate generator.

For now, would keep it as a LC test and do only the minimal prep work to allow tests against BlockBody on top of State. If we need more generalized testing in the future, it's a point that can be re-evaluated when there is a need for it, though.