Cardano Updates

The only uses of BlobRef.readBlob were in the context of withWeakBlobRef
so we can go straight to a helper function that does just that.

Also remove now-unused WriteBufferBlobs.readBlob

Not yet used in this patch.

Also move the BlobSpan defintion to this module.

Currently, pre-snapshots, the Run does _not_ delete its blob files when
the run is closed, but the WriteBufferBlobs _does_ delete its blob file.

Insert a temporary hack to accomodate this. This commit can be reverted
as part of implementing snapshots properly.

Where before it contained a file handle and a ref counter, it now just
contains a BlobFile (which itself is the pair of a handle and counter).

Originally it contained the file handle and the refcounter of either the
Run or write buffer that the blob ref came from (pointed to).

In a previous patch we changed the Run and WriteBufferBlobs to
themselves contain an independently ref-counted BlobFile, and so at the
same time the blob ref refcount refers to the blob file refcount not
the refcount of the parent object.

In this patch we now change RawBlobRef to directly hold a BlobFile. This
makes the representation logically more uniform between the run and
write buffer cases: since we now just point to the BlobFile being held
by each blob source.

This refactoring will make things much clearer once we switch the
representation of ref-counted objects. Since we'll maintain a reference
to a BlobFile rather than a lower-level combo of a file handle and
reference count.

Signed-off-by: Francisco Javier Ribo Labrador <[email protected]>

Signed-off-by: FabioPinheiro <[email protected]>
Signed-off-by: Francisco Javier Ribo Labrador <[email protected]>

Signed-off-by: Francisco Javier Ribo Labrador <[email protected]>

Signed-off-by: Francisco Javier Ribo Labrador <[email protected]>