EVM on WASM: Refund gas for nested contract calls

Context

When one contract calls another, it allocated a number of gas units for that call. After the call is finished, unused gas is refunded to the calling contract in a way so that it can use the refunded gas further in the same transaction (as opposed to refunds from freeing up storage, which cannot be used in the same transaction).

Manually testing the MR

Use the unit tests. They have updated gas cost for relevant tests. Run CI.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR