There were several problems related to dumping state.
- If a preimage was missing, even if we had set the `OnlyWithAddresses` to `false`, to export them anyway, the way the mapping was constructed (using `common.Address` as key) made the entries get lost anyway. Concerns both state- and blockchain tests.
- Blockchain test execution was not configured to store preimages.
This changes makes it so that the block test executor takes a callback, just like the state test executor already does. This callback can be used to examine the post-execution state, e.g. to aid debugging of test failures.
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