Show cache alias instead of backend repr in calls table

[federicobond]

Description

This changes the values of the backend columns for cache calls in the Cache panel from <django.core.cache.backends.dummy.DummyCache object at 0x1063950a0> to default or the corresponding alias. This makes it much easier to identify which call is made to which backend when several cache backends share the same engine.

Before:

After:

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

[tim-schilling]

@federicobond I spotted a few more clean-ups, but this is on the edge of being good to go. Thank you for being patient!

[tim-schilling]

@federicobond I removed the _djdt_patched attribute since it was causing confusion in the tests of when the cache integration had been patched or not. I also added in a suffix of (BackendClassName) to the rendered text. I figure some people would benefit from knowing what backend class is being used. If the tests pass, I'm happy to merge this.

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
debug_toolbar/panels
cache.py					98
Project Total

This report was generated by python-coverage-comment-action

[tim-schilling]

Squashed the commits and merged. Thank you @federicobond!