[conformance + storage] Capture Storage Run

[patrick-ogrady]

It would be VERY impactful to capture the value of writing some set amount of data to some storage implementation and assert that what is stored on disk (after sync) is exactly the same.

This could be implemented by implementing a StorageConformance helper (like CodecConformance) that just implements Blob (avoiding the need to create an entire runtime).

[patrick-ogrady]

Added storage_audit() in #2707 to make this easier!