The data type of IdTime is 'Optional[float]' [1], [2]. Before this patch the
msgpack decoder could only decode 'IdTime' in case its data type was
'float'. Now it also supports the decoding of IdTime in case it is NIL.

[1] See here, the fifth argument is IdTime:

    https://lab.nexedi.com/nexedi/neoppod/-/blob/3ddb6663/neo/master/handlers/identification.py#L26-27

    This is found to be 'Optional[float]':

    https://lab.nexedi.com/nexedi/neoppod/-/blob/3ddb6663/neo/tests/protocol#L98

[2] This seems to be true for both, pre-msgpack and post-msgpack
    protocol, because in the pre-msgpack NEO/go there is already this
    note:

    https://lab.nexedi.com/kirr/neo/-/blob/1ad088c8/go/neo/proto/proto.go#L352-357