rebase; extract factories and the mocks they are dependent on to

libraries/shared; adjust omni test_helpers to drop and recreate
checked_headers table to avoid reaching 1600 column limit after repeated
tests (dropping columns doesn't actually remove them from contributing
to that limit)

libraries/shared/storage/utils/value.go

@@ -26,12 +26,6 @@ const (
 
 type Key string
 
-const (
-	Ilk  Key = "ilk"
-	Guy  Key = "guy"
-	Flip Key = "flip"
-)
-
 type StorageValueMetadata struct {
 	Name string
 	Keys map[Key]string