Change callProc/createWriteStatement to H.Snippet.
Parametrize the inputs on the same SQLFragments by taking advantage
of hasql-dynamic-statements. It's not necessary to parametrize
every input, inlining with pgFmtLit can still be used for queries
that can't be parametrized(like SET LOCALs).
Also adds hasql-dynamic-statements to Nix and stack.