Update save_npy/load_npy, add STORAGE_MAP & get_tosa_dtype_mapping

- Updated save_npy to ensure that the array's dtype matches
the expected storage type.
- Revised load_npy to verify and convert the loaded arrays
dtype to the expected internal type based on the provided TOSA DType.
- Added a new STORAGE_MAP mapping TOSA DType values to their
corresponding internal mldtypes and NumPy storage types.
- Introduced get_tosa_dtype_mapping() to expose a user-friendly
mapping of TOSA dtypes to internal and storage types.

Signed-off-by: Eirene Vlassi Pandi <eirene.vlassipandi@arm.com>
Change-Id: I6be1446a01e2a9f0861766d1c0488627042eadce