[Junie]: Junie Push cache backend checks down to backend classes

[junie-eap]

📌 Hey! This PR was made for you with Junie, the coding agent by JetBrains Early Access Preview

It's still learning, developing, and might make mistakes. Please make sure you review the changes before you accept them.
We’d love your feedback — join our Discord to share bugs, ideas: here.

• 🔗 Issue: Junie Push cache backend checks down to backend classes #4
• 🏷 Title: Junie Push cache backend checks down to backend classes

📝 Original Issue Description

  Issue task:
  Description 

Currently, the three system checks for caches are individual functions ​in ​django.core.checks.caches. But two of them relate only to FileBasedCache, yet still run regardless of which backends are used. This structure causes some issues:

FileBasedCache and its dependencies are imported even when not used.
Some waste in check_cache_location_not_exposed() when no FileBasedCache is configured, which resolves some paths before checking against caches.
The code structure is a bit messy with repeated loops and isinstance(cache, FileBasedCache) conditions.
I propose restructuring these checks to live within the cache backend classes in django.core.cache.backends.*, adopting the same pattern used for model and field checks, admin checks, and staticfiles finders. (And template backend checks, as I proposed in #35233.)

This would mean:

Adding BaseCache.check() which just does return [] for now.
Pushing the existing two checks down to a new FileBasedCache.check() method.
Dropping the existing code.
Checking tests cover the checks sufficiently and they pass with the new structure.
Potentially adding a test to cover a custom cache backend with its own check.
According to the ticket's flags, the next step(s) to move this issue forward are:

To add tests to the patch, then uncheck the "Needs tests" flag on the ticket.
To write documentation for the patch, then uncheck "Needs documentation" on the ticket.
To improve the patch as described in the pull request review comments or on this ticket, then uncheck "Patch needs improvement".
If creating a new pull request, include a link to the pull request in the ticket comment when making that update. The usual format is: [https://github.com/django/django/pull/#### PR].

  Issue comments:
  No comments yet

📊 Junie Summary

The cache system checks in Django were restructured by adding a check() method to BaseCache and moving related checks to FileBasedCache, consolidating standalone functions into check_cache_backends. Tests were updated to ensure correct implementation, though they could not be run due to environment limitations. No documentation updates were needed.