Implement a function has_empty_storage in BaseRuntime.

[MathieuDutSik]

Motivation

For the purpose of testing if a contract exists in EVM, we introduce the functionality of testing if a contract
has empty storage.

Proposal

The following is done:

• The functionality is added to the BaseRuntime.
• It uses the TotalStorageSize in the execution_state_actor.rs.
• It uses the view.total_size() of the KeyValueStoreView.
• The functionality is provided to the Wasm smart contracts.

Several points have to be noted:

• The Wasm smart contracts are persistent. Only at the end with the self.state.save().await does their state become observable. This point is exemplified in the example test.
• So, if a contract is writing its state only at the fn finalize step, then we cannot see that its state is non-trivial only at the next block.
• The designed use case for this feature is EVM smart contracts. Fortunately, for those contracts, we are writing the state directly to the storage and we are not waiting for fn finalize. So, that is fine here.

Test Plan

The CI.

For testing the has_empty_storage, we implemented separately some end-to-end tests.
They have not been put in the PR, since you need two contracts:

• one that gets instantiated
• and one that does the has_empty_storage.

Release Plan

This does not appear to be TestNet breaking.

Links

The test is implemented in test_has_empty_state