revert Manifest and Block to ref objects to avoid triggering broken sink/move semantics

codex/blocktype.nim

@@ -31,7 +31,7 @@ import ./codextypes
 export errors, logutils, units, codextypes
 
 type
-  Block* = object
+  Block* = ref object
     cid*: Cid
     data*: seq[byte]
 

codex/manifest/manifest.nim

@@ -29,7 +29,7 @@ import ../logutils
 # TODO: Manifest should be reworked to more concrete types,
 # perhaps using inheritance
 type
-  Manifest* = object
+  Manifest* = ref object
     treeCid {.serialize.}: Cid              # Root of the merkle tree
     datasetSize {.serialize.}: NBytes       # Total size of all blocks
     blockSize {.serialize.}: NBytes         # Size of each contained block (might not be needed if blocks are len-prefixed)