Use frozendict package instead of custom FrozenDict class

[redeboer]

In ComPWA/ampform#444 (comment) it became clear that the pickled form of FrozenDict (and therefore of Topology, ReactionInfo etc.) does not have a stable hash (as computed with xxhash). The frozendict package does provide a stable hash, so it should be tested whether FrozenDict can be replaced by it.