feat: cache simple repository pages (#6932)

At #5868, I
[suggested](https://github.com/python-poetry/poetry/pull/5868#discussion_r931507885)
that some of the caching that was being reworked could be removed
altogether, because cachecontrol was already taking care of it just
fine.

But now I find myself using an Azure artifacts repository, and it is
returning headers that insist that the client does not do any caching:
```
cache-control: no-cache
pragma: no-cache           
x-cache: CONFIG_NOCACHE 
```
(pypi, by contrast, sets max-age to 10 minutes here).

So I was wrong! And now I am seeing a big performance hit in some
projects where the solve involves overrides and backtracking: and
therefore hitting the legacy simple API repeatedly.

However, we don't need all the mechanism of cachy and its like for this,
a well-placed `@lru_cache()` seems more than sufficient.

This makes me wonder whether it wouldn't be better to do similar for
pypi anyway, and rip out cachecontrol altogether. But let's keep it
simple for now: this is an easy fix to a performance regression.