CLN: Standardize indentation and alphabetize deps
I can't fix a problem that makes zero sense to me (#18089), but in the interests of being a team player, I can try to contribute around the periphery.

This just takes the `ext_data` dict and a) standardizes the indentation, b) arranges the entries in alphabetical order.  It is straightforward to check that the version of the dict here `==` the version in master.  The main reason to do this is so that the diff in the next step is easy to review.  

The next step is to go through and identify pyx files that don't cimport _anything_  e.g. `_libs.testing` and fill out their `ext_data` entries with the appropriate `[]`s (note that the processing of `ext_data` inserts default values for missing keys, so adding `[]` entries _is_ part of the specification).

There are a few modules that meet that description, then a handful of others that only have cimports from numpy (e.g. io.sas._sas).  Those entries can be fully filled out independently of any other outstanding issues.