feat: type spec tests

[Zacholme7]

Issue Addressed

#39

Proposed Changes

1. This sets up a register/loader based approach for the spec tests where each test implements the SpecTest trait so that we able to properly load in the correct input json files and have a simple way to setup and run each test file

2. This nearly completes the type spec tests that are relevant to our implementation. These tests are all pretty straightforwards and I dont anticipate any errors with the remaining ones so we may want to just remove them or finish them up if time permitting.

I would say the main use for these is to test our SSZ encoding/decoding, which we can now confirm is spec compliant. There really may even be an argument that we should only include the ssz encoding/decoding and consider what we can scrap.

Change summary

1. All of the changes in common/ssv_types/src just deal with de-serializing the types for the spec tests
2. in spec_tests/src/types are all of the spec tests and they follow the same pattern. Have a struct for parsing in the data that implement the SpecTest trait for a clean interface to run the test and get its type
3. spec_tests/src/utils just contains some extra de-serializers that are needed
4. spec_tests/src/lib.rs is the core brain for loading and running the tests. A test gets registers in the TEST_LOADERES which makes it so that the run_tests function can properly extract the correct files to load in for each test variant

Note: We need allow(dead_code) at the top of lib.rs as this code is just used for testing so clippy marks it as un-used when it is actually used. Ive done a walkthrough and manually checked the usage of everything