[RPC] Fix bug in Cryptol JSON -> Python for records, add test

[m-yac]

This PR:

• Fixes a bug which would result in incorrectly converting a record value from Cryptol JSON to Python.
• Adds a new test test_types.py which would have detected this bug, and will detect any future changes to the way basic Cryptol types are handled.

While making this change I also noticed that there were some missing calls to .result() in test_AES.py and that test_DES.py had a typo. These two fixes are also included in this PR.

[m-yac]

Should I be worried that the CI failed? The RPC tests all passed on ubuntu, but failed on macos with:

======================================================================
ERROR: test_CplxQ (test_CplxQNewtype.TestCplxQ)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/runner/work/cryptol/cryptol/cryptol-remote-api/python/tests/cryptol/test_CplxQNewtype.py", line 13, in test_CplxQ
    forty_two = c.eval("fortyTwo").result()
  File "/Users/runner/Library/Caches/pypoetry/virtualenvs/cryptol-L3Aq5hhJ-py3.7/lib/python3.7/site-packages/argo_client/interaction.py", line 168, in result
    return self.process_result(self._result_and_state_and_out_err()[0])
  File "/Users/runner/Library/Caches/pypoetry/virtualenvs/cryptol-L3Aq5hhJ-py3.7/lib/python3.7/site-packages/argo_client/interaction.py", line 153, in _result_and_state_and_out_err
    raise self.process_error(exception)
argo_client.interaction.ArgoException: Unknown state ID 24bf76c8-1207-4b9c-8709-2e73caa435cd

This test works just fine on my (macos) machine.

[atomb]

That's a known bug that I think @pnwamk is working on fixing separately.