Test that Haskell code lenses resolve onto notebook lines

[thomasjm]

Covers parts 1 and 2 of #120 end to end, via getAndResolveCodeLenses — the same path codedown uses.

• x :: Integer resolves onto notebook line 1 and foo :: IO () onto line 3.
• No lens comes back on line 0, where hnls rewrites a bare expression into a generated binding, and none has an expr… title.

Verified against a locally built hnls carrying both fixes: both tests pass. Against an hnls without the codeLens/resolve transform they fail with ghcide-type-lenses: Stale Resolve, which is the symptom in the issue — so this does discriminate.

Do not merge until hnls is released with the fix and hnls-version.nix is bumped. The released binary doesn't have it yet, so this will fail on main until then.