gh-37839: Cythonize `GraphicMatroid`
A metamorphosis of `graphic_matroid.py` into `graphic_matroid.pyx` and
`graphic_matroid.pxd`.
Things should be somewhat faster; test, e.g., the `GraphicMatroid`'s
`_circuit` function. An indirect and diluted test that shows improvement
can be seen by running `%time matroids.CompleteGraphic(8).circuits()`
(~half the time).
`For the reviewer:` The changes of this PR are only inside the
`matroids` module. The rest come from #37835.
### :hourglass: Dependencies
#37835: Deeper improvements of `DisjointSet`.
URL: https://github.com/sagemath/sage/pull/37839
Reported by: gmou3
Reviewer(s): gmou3, Kwankyu Lee, Travis Scrimshaw
