Release 1.4.0 breaks storage format

[sebastianburckhardt]

one of the changes in #275 seems to have broken the data contract, causing checkpoint loads to fail with exceptions like this:

: Part06 !!! Faster Storage Error : loading checkpoint : System.Runtime.Serialization.SerializationException: Error in line 1 position 258. Expecting state 'Element'.. Encountered 'Text'  with name '', namespace ''. 
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.HandleMemberNotFound(XmlReaderDelegator xmlReader, ExtensionDataObject extensionData, Int32 memberIndex)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.GetMemberIndexWithRequiredMembers(XmlReaderDelegator xmlReader, XmlDictionaryString[] memberNames, XmlDictionaryString[] memberNamespaces, Int32 memberIndex, Int32 requiredIndex, ExtensionDataObject extensionData)
   at ReadValueTupleOflongintFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 id, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   at ReadValueTupleOflongValueTupleOflongintU6ho3BhdFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 id, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   at ReadDedupStateFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString[] , XmlDictionaryString[] )
   at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 id, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
   at ReadArrayOfTrackedObjectFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString , XmlDictionaryString , CollectionDataContract )
   at System.Runtime.Serialization.CollectionDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
   at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, DataContract dataContract, String name, String ns)
   at System.Runtime.Serialization.DataContractSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
   at System.Runtime.Serialization.XmlObjectSerializer.ReadObject(XmlDictionaryReader reader)
   at DurableTask.Netherite.Serializer.DeserializeSingletons(Stream stream) in /_/src/DurableTask.Netherite/Util/Serializer.cs:line 84
   at DurableTask.Netherite.Faster.FasterKV.<RecoverAsync>d__36.MoveNext() in /_/src/DurableTask.Netherite/StorageLayer/Faster/FasterKV.cs:line 241