Implement remaining parts of the spec

[ralexstokes]

There are parts of the consensus-specs this repo currently does not support.

A notable chunk are the networking specs, but support is only in place on an as-needed basis.

There are a number of spec tests we currently ignore as the relevant specs are not implemented:

• #351
• #352
• #353
• #354

There are also sync spec tests, but I don't expect this repo to support that functionality anytime soon.

A PR to implement the spec and the corresponding spec tests for one of these categories would be amazing!