Cardano Updates

Make `WriteBufferBlobs` functions exception safe

Make `BlobFile` functions exception safe

Rename Merge.Level to MergeType and extend with MergeUnion enum value

QLS: catch missed disk fault errors

QLS: check `NoThunks` only at the end of an action sequence

Display action registry exceptions in human-readable format

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

This is closer to a depth-first order. First introduce everything for
the regular levels, then the union level and merging tree.

This follows the naming scheme from the prototype.

This just adds the new enum (and renames) but does not introduce any new
merging behaviour yet, and the new MergeUnion value is not used (except
in snapshot (de)serialisation).

It is not used in MergingRun. And it should not live there because
MergingRun is shared between level merges and union merges, but a policy
for a level is obviously level specific.

In Test.Database.LSMTree.Internal.Snapshot.Codec, import the general
Database.LSMTree.Extras.Generators and use several of the arbitrary
instances from there. Remove ones that were duplicates, and remove
overlapping instances.

`s-r-p` for `quickcheck-lockstep` with more verbose counterexamples