* feat: add lfu cache
* docs: add comments and explanation to class LFUCache
* test: add tests for class lfu cache
* docs: document namespace and classes
* test: modify tests to check negative numbers
* docs: document template params and class data members
* test: make test func static and move tests in the same func
---------
Co-authored-by: realstealthninja <68815218+realstealthninja@users.noreply.github.com>
