`.objType` and `.dtype` properties for Arkouda Classes

[Ethan-DeBandi99]

This issue is stemmed from conversation in #1374.

Add .objType and .dtype to each Arkouda class.

• .dtype is the numpy dtype of a single element of the array, e.g. what numpy dtype would x[0] have? This is limited to {np.int64, np.uint64, np.float64, np.bool, np.str_}. For example, a Categorical would have dtype np.str_ because single element access returns a string.
• .objtype is the logical, human-understood type of the whole array, e.g. pdarray, Strings, Categorical, IPv4.

This issue is intended for tracking. Initially, Categorical will be updated as a trial. Once that has been completed and decision to move forward has been made, we will add a list of classes to update.

[stress-tess]

This issue is related to #1385