Un-break nix build + nix develop

[jisantuc]

On main, nix build fails with missing random >=1.3 && <2. That makes sense, since the version of random in haskellPackages in the flake inputs was 1.2.x. This PR overrides random in hsPkgs to pin to 1.3.1 instead. A consequence of that was that time-compat tests broke, because they depend on random between 1.2 and 1.3, so it also overrides time-compat to skip tests.

This PR also updates the dev shell to provide a little more power. On main, if you nix develop, you get vanilla cabal without any knowledge of the project's dependencies, e.g.

$ cabal repl
Warning: The package list for 'hackage.haskell.org' does not exist. Run 'cabal
update' to download it.
Resolving dependencies...
Error: [Cabal-7107]
Could not resolve dependencies:
[__0] trying: dataframe-0.4.0.10 (user goal)
[__1] unknown package: zstd (dependency of dataframe)
[__1] fail (backjumping, conflict set: dataframe, zstd)
After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: dataframe, zstd

After changes in this PR, the dev shell is aware of the dataframe package, and cabal repl drops you into a shell with all of the project's modules, so if you have foo.csv like

a,b
1,2
3,4

you can

$ cabal repl
[...]
ghci> import DataFrame.IO.CSV
ghci> readCsv "foo.csv"
---------
 a  |  b
----|----
Int | Int
----|----
1   | 2
3   | 4

[collinarnett]

LGTM