STY: standardize spacing for casting, with linting

[jbrockmendel]

Casting in cython is done with the syntax <type>obj or <type> obj. ATM the code uses both of these. This PR standardizes on the first usage, with a lint check.

@datapythonista I'm not sure whether the grep check here belongs in the patterns section or in the non-python section. LMK if you have a preference.

[jreback]

nice

prob should put all of these rules into a flake-cython package :)

[jbrockmendel]

prob should put all of these rules into a flake-cython package :)

If we can find someone else to maintain it, that'd be fantastic.

[codecov]

Codecov Report

Merging #23474 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #23474   +/-   ##
=======================================
  Coverage   92.23%   92.23%           
=======================================
  Files         161      161           
  Lines       51197    51197           
=======================================
  Hits        47220    47220           
  Misses       3977     3977

Flag	Coverage Δ
#multiple	90.61% <ø> (ø)	⬆️
#single	42.27% <ø> (ø)	⬆️

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[jbrockmendel]

Not for this PR, but a couple of other patterns that would be relatively easy to lint for:

cimport numpy as np --> should be cnp (not a widely-used convention, but it should be)
* imports
number of lines after function/class

For these purposes (and for this PR) we just assume away comments and docstrings.

[datapythonista]

Thanks @jbrockmendel, nice addition.

There are reasons for having it with both the linting and the patters, happy with any.