Specialiser creates specialisation assuming local equality

Carrying on from #23109

I have extracted a reproducer for that issue which doesn't depend on anything in horde-ad so it's much simpler. It still needs to depend on the plugins though but I suspect that the plugin dependencies can also be removed.

https://github.com/mpickering/crispy-computing-machine

If you compile with ghc-9.6.1 you get

32
repro: Bad runtime result
CallStack (from HasCallStack):
  error, called at Main.hs:11:57 in main:Main

The problem is along the lines of:

• In the call to spec we specialise tbuild' for @33 and @0.
• In the body of $stbuild' (in the recursive call to the specialiser), in the binding of buildSh, there is a call to typeRep (Proxy @ix), the specialiser creates a bogus specialisation here.

"SPEC/TestHighRankSimplified typeNatTypeRep @_"
    forall (@(ipv_i1oF :: GHC.TypeNats.Nat))
           ($dKnownNat_s1HG :: GHC.TypeNats.KnownNat ipv_i1oF).
      base:Data.Typeable.Internal.typeNatTypeRep @ipv_i1oF
                                                 $dKnownNat_s1HG
      = $stypeNatTypeRep_s1HJ @ipv_i1oF

• Then spec3 rewrites using this specialisation giving a bogus result.

Perhaps someone can help either removing the dependency on the plugins or further minimising it.