[Feature Request] Improving and Adding new functions to CuPy Statistics

**Usage**
Statistical functions are widely used by Data Scientists. Having an API like scipy.stats in CuPy is always helpful. Since most of the calculations involve matrix operation and mathematical calculations, they can be GPU accelerated. Some of the functions are covered in the statistics module.

**Proposal**

If approved, I would like to start with implementing Correlation functions and Summary statistics since they are relatively less complex and useful. Please refer to the list of functions used here https://docs.scipy.org/doc/scipy/reference/stats.html

Thanks,
Anudeep.

Start with CuPy's statistics module and the linked SciPy stats reference to identify the proposed correlation and summary functions. Clarify the initial function list and expected SciPy-compatible behavior before implementation; done means the agreed functions are available in CuPy with validation against their stated behavior.

Written by the indexing model from the issue text.