Fix incorrect cache hit/miss reporting for cache.get()

[Harsh3006]

Description

This change fixes incorrect cache hit/miss reporting in the Cache panel for cache.get().

Previously, the Cache panel determined whether a cache.get() call was a hit or a miss solely based on whether the returned value was None. This resulted in two incorrect scenarios:

A missing key with a supplied default (for example, cache.get("missing", "default")) was reported as a cache hit, even though the value was not retrieved from the cache.
A cached value of None was reported as a cache miss, even though the key existed in the cache.

The Cache panel now correctly distinguishes between a missing cache key and a cached value equal to the caller's supplied default while preserving the existing cache.get() behavior.

Fixes #2417

Checklist:

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

AI/LLM Usage

• This PR includes code generated with the help of an AI/LLM

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
debug_toolbar/panels
cache.py					127, 166-167
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