Test and handle side effects of ProviderConfig::genesis_state

[Wodann]

In #755 we added support for setting a "genesis state" for a blockchain. This can have one of two effects:

• For a local blockchain, it sets the genesis state
• For a forked blockchain, it overwrites the forked state

The former is always safe, but the latter might introduce unexpected side-effects when incorrectly overwriting accounts or storage. We should add tests to make sure we're gracefully handling those error states.

Definition of Done

• Full branch coverage for usage of the genesis_state in the construction of ForkedBlockchain (in the provider data)