Add comprehensive unit tests for ContributionHeatmap (#2751)

* Add unit tests for ContributionHeatmap component

* Updating the math.random() function

* removing the usage of void operator and array index in keys

* Refactor ContributionHeatmap tests for improved readability and consistency

* Refactor ContributionHeatmap tests to enhance clarity and remove unnecessary comments and removing the use of require

* Refactor tooltip test to remove void operator and improve clarity

* Refactor tooltip mock to simplify custom tooltip handling and remove unnecessary checks

* Refactor ContributionHeatmap test to improve test description for clarity

Author: Swyamk