Improve server startup time by serializing graph to/from disk using `GHC.Serialized.serializeWithData`

[runeksvendsen]

https://downloads.haskell.org/ghc/latest/docs/libraries/ghc-boot-9.12.1-2bb4/GHC-Serialized.html#g:3

Seemingly a GHC-specific format, so include GHC version (or --info output?) in a header.

JSON deserialization seemingly can't be made sufficiently performant.

https://downloads.haskell.org/ghc/9.8.1-alpha4/docs/users_guide/using.html#ghc-flag---info

[runeksvendsen]

Update

GHC.Serialized.serializeWithData is horribly slow. Consider using e.g. https://github.com/jberthold/packman instead.