Added support for business logic tests

What's Changed

Added business logic specifications to allow testing:

• Deciders,
• Command handlers,
• Event Sourced entities./aggregates,
• State-based entities/aggregates.

See the documentation: https://github.com/oskardudycz/Ogooreck/tree/main#business-logic-testing.

by @oskardudycz in #9, #10

Full Changelog: 0.3.0...0.5.0