Add fuzzy test for teerex pallet

[Niederb]

The teerex pallet already contains some complex parsing logic (certificates, sgx data structures, ...) and the addition of DCAP will lead to even more parsing logic.
Given that any issue in the pallet have security implications and a panic in the pallet would be severe for the blockchain I think we should think about adding some fuzzy tests.

• The pallet interface (just a vec of u8) is very simple so it should be quite easy
• I think in the long run this could also be interesting for some of our other interfaces (RPC calls, externalities, ...)

[Niederb]

There are now some fuzzy tests but they are not executed in an automatic fashion. So there are some additional steps needed:

• CI integration
• How to handle the corpus of test cases
  • Can the CI expand the corpus? How?
  • It would be very valuable to have a test for verify_dcap_quote(...)