Remove premature caching of lookups for unused lint

[som-snytt]

Caching a lookup of c in a.b.c is ok at a.b.
A lookup from a.p should not see the cached value.

Fixes #22971

[som-snytt]

Flaky cats test.

[som-snytt]

This deals with the second-hardest problem after naming, but also the performance of the lint requires review, since this is an example of premature caching without benchmarking.

It might be preferable to ignore caching (for the sake of correctness) and only then do a review of performance. That also entails a review of architecture and whether mini-phase really serves the use case.

[som-snytt]

As coded, the cache of lookups at contexts doesn't pull its weight, either provably or demonstrably.

This commit removes it for robustness. (The first swing tweaked a couple of conditions that made the test pass.)

The phase still needs a review of performance.

[som-snytt]

Took me a while to see that the REPL wrapper test needed adjustment because there is no longer a fresh context "injected" to house the cache apparatus.

[noti0na1]

LGTM, just need to rebase to main