Cardano Updates

MergingRuns in incoming runs and MergingTree allow for different types
of merges. We can statically enforce the related invariant.

This fixes the file paths errors for the write buffer blobs.

It is also generally the right direction to go: If we ever want these
tests to work with a write buffer and blobs, lookups must look at the
original write buffer blobs, not an empty one.

The minimum length of keys for the compact index increased from 6 to 8
bytes at some point.

Also, releasing a run was changed to remove the files associated with
it. The cleanup code was manually doing the same, which then became
unnecessary and started causing issues.

Merge micro bench: release run during cleanup only

Renumber run and write buffer files starting from 0 in snapshots

We will however still supply union credits to tables with a union debt
that has already been fully paid off (tree merge got completed). This is
difficult to avoid, since the model doesn't know how much work it is to
complete a particular tree/union merge.

We will however still supply union credits to tables with a union debt
that has already been fully paid off (tree merge got completed). This is
difficult to avoid, since the model doesn't know how much work it is to
complete a particular tree/union merge.