This PR fixes an issue with using a non-default compression method. The recreate database will detect the compression module correctly and restore everything. But when recreating the database it will look at the `compression-module` from the given options and persist this value into the database.
If the recreate was made without passing in the compression module in the options, the default compression module would be persisted to the database, which would later cause problems for operations that rely on this value.
With this PR there is a test for the behavior, and the compression module is extracted from the first volume, similar to how blocksize and other options are written back.
In some cases it is possible for the index volumes to be created with empty block lists. If this happens, the reader would fail as the strict JSON parsing would encounter an unexpected token.
With the fix, the code now correctly reads such JSON documents and some variants.
Added a number of tests to make sure these cases are correctly reproduced.
This fixes#6892
Update the SQL to also group on size (just in case).
Renamed the normal read method to signal that it is unverified.
Made the verified reader use enumeration state machine to avoid materializing the list.
`var`-ified some of the test code.
While this does not affect any behavior, it more accurately describes
the accessibility. Since abstract classes can only be instantiated by
an instance of a derived type, the constructors should at most have
protected access.
Kenneth Skovhede