fix!: Update testing helpers

[flavio]

The testing package used to contain some helper methods and types that could be used inside of policy unit tests.

The module defined objects that are now defined inside of the protocol package thanks to us leveraging easyjson.

The testing code has been updated to:

• Remove types that are now declared inside of the protocol package
• Update the functions to make use of the new types used by policies

This is a breaking API change that is going to break old policies unit tests.