Investigate if we should keep Declare cheatcode

[cptartur]

@MaksymilianDemitraszek suggested that we should remove declare cheatcode entirely, and implicitly declare all contracts from the project when running a test runner.

This might be a good approach, but there are some open questions:

• how should declaring work if the user doesn't know the class hash
• how to actually get the class hash of declared contract
• what in the case where user doesn't want to have their contract declared automatically for whatever testing reasons