…py#29333)

* BUG: Always return a real dtype from linalg.cond.

Addresses numpygh-18304.

The condition number of a matrix is the product of two norms, which are
always non-negative and real-valued, so the condition number itself
should be non-negative and real-valued. This commit returns the proper
real dtype from `linalg.cond`, and includes tests for the condition
number of a complex matrix in various norms.

* ENH: Change type of complex results only.

This commit addresses a reviewer comment on the blanket application of
`abs(r)`. It specifically ensures the return type of complex-valued
matrices will be the corresponding real type.