Add unit tests for pkg/util/client/cache.go

[GautamBytes]

This PR introduces a new test file, cache_test.go, to provide comprehensive unit test coverage for the custom cache implementation located in pkg/util/client/cache.go.

The new tests cover the following key areas:

Cache Creation: Verifies the NewCache function under various configurations, including default and custom schemes.

List Logic: Tests the branching logic of the internalCache.List method, ensuring it correctly handles the DisableDeepCopy option and the associated disable-no-deepcopy global flag.

Helper Functions: Validates helper utilities like isDisableDeepCopy and the no-op ApplyToList method to ensure complete coverage.

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[GautamBytes]

@ringtail , @chrisliu1995 will you rerun the workflow they seem to be unrelated to my pr , it will pass then. Also , review this whenever feasible!