Add a `.clear_cache` and `.clear_task_cache` method to avoid the need to manually delete the cache.

[Logiquo]

.clear_cache should clear the dataset cache (including its corresponding task cache)
.clear_task_cache should only clear the related task cache based on (dataset, task) pair.

We want to prefereably implement this after #764 to allow more accurate task cache deletion.

[Eshaan-byte]

@Logiquo, can you assign me

[Eshaan-byte]

PTAL @Logiquo