Prevent summarizing JAX PRNG key dtypes.

Numeric dtypes can be summaried by outputting summary statistics (e.g. min, max, avg, sparsity), but we do not produce any summary for extended dtypes like JAX PRNG key dtypes. However, the existing implementation still tries to convert the arrays to numpy for faster summarization even if the dtype cannot be summarized, which produced an error. This commit disables summarization fully for these dtypes so that they can be rendered as normal. Fixes #52.