feat(users/Profpatsch/netencode): Add initial Haskell parser

A simple categorical parser that does not implement Monad, and does
not contain an `m` and some rudementary error message handling.

In the future I’d probably want to wrap everything in an additional
`m`, so that subparsers can somehow use `Selective` to throw errors
from within `m` that contain the parsing context if at all possible.
Hard to do without Monad, I have to say. Not even stuff like `StateT`
works without the inner `m` implementing `Monad`.

Change-Id: I1366eda606ddfb019637b09c82d8b0e30bd4e318
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7797
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/netencode/default.nix

@@ -18,6 +18,7 @@ let
     src = depot.users.Profpatsch.exactSource ./. [
       ./netencode.cabal
       ./Netencode.hs
+      ./Netencode/Parse.hs
     ];
 
     libraryHaskellDepends = [