add isspace function to match numpy function for ndarrays:
https://numpy.org/doc/stable/reference/generated/numpy.char.isspace.html

Returns true for each element if there are only whitespace characters in the string and there is at least one character, false otherwise.

May rely on chapel function isSpace:
https://chapel-lang.org/docs/language/spec/strings.html?highlight=istitle#String.string.isSpace