Changed cache monkey-patching for Django 3.2+

[tim-schilling]

Changed caching monkey-patching for Django3.2+ to iterate over existing
caches and patch them individually rather than attempting to patch
django.core.caches as a whole. The middleware.cache is still
being patched as a whole in order to attempt to catch any cache
usages before enable_instrumentation is called.

Fixes #1496

Big thanks to @LiorA1 for reporting the issue and creating a reproducible test case.

[codecov]

Codecov Report

Merging #1497 (060860a) into main (6d3eb44) will decrease coverage by 0.89%.
The diff coverage is 39.39%.

@@            Coverage Diff             @@
##             main    #1497      +/-   ##
==========================================
- Coverage   86.61%   85.72%   -0.90%     
==========================================
  Files          35       35              
  Lines        1868     1891      +23     
  Branches      262      272      +10     
==========================================
+ Hits         1618     1621       +3     
- Misses        178      190      +12     
- Partials       72       80       +8     

Impacted Files	Coverage Δ
debug_toolbar/panels/cache.py	72.56% <39.39%> (-9.71%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6d3eb44...060860a. Read the comment docs.

[tim-schilling]

Shoot. This still needs to monkey-patch django.core.cache.caches for other caches that get created after enable_instrumentation is called.

[tim-schilling]

Shoot. This still needs to monkey-patch django.core.cache.caches for other caches that get created after enable_instrumentation is called.

That would require changing the settings which is a no-no. So I was right the first time.

[tim-schilling]

The reduction in code coverage is because our report doesn't handle the coverage across different versions (I think).

[matthiask]

The reduction in code coverage is because our report doesn't handle the coverage across different versions (I think).

I can't say for sure but I think you're right.