Deserializing many TypeReps may lead to high residency

Deserialized `TypeRep`s don't share any structure with each other, which can potentially waste a lot of space. For example, if I fill a giant `Set` with deserialized `Dynamic` values, the lion's share of the space could be taken up by the `TypeRep`s. One potential fix would be to maintain weak tables holding deserialized `TyCon`s and `TypeRep`s. We could use one of type `Map Fingerprint (exists a. Weak (TypeRep a))` and one of type `Map Fingerprint (Weak TyCon)`, but other sorts of maps would probably be faster. When a (perhaps recursively) deserialized `TyCon` or `TypeRep` matches one stored in the table, it would be thrown away in favor of the stored one.