Add support for displaying numpy scalars

[peytondmurray]

This PR adds support for displaying the values of numpy scalars. Closes #744.

Following the pattern set forth elsewhere in python_data_access.rs, I used the raw pointer address of the numpy scalar to be printed. Since numpy scalars all have similar structs, e.g.

{
    ob_base: PyObject,
    obval: <value>
}

where obval can be of different sizes, I just advance the pointer to the scalar by the size of PyObject, and then use the value_type_name to know how many bytes to read. This approach avoids the need to generate numpy bindings, though if the structure of numpy scalars changes in the future we'll have to update.

Note that this only works for uint8-64, int8-64, float32-64, and bool types; other types are not printed (half-precision and 128-bit floats aren't supported with native rust types yet although there is an RFC for them, and neither are complex numbers).

[peytondmurray]

Hey, just saw this - thanks for helping this across the finish line 🎉

[benfred]

thanks for the PR!