some formatting for NOTE:: blocks

<div id="comment:0"></div>

mostly in pyx files

Component: **documentation**

Author: **Frédéric Chapoton**

Branch/Commit: **[`8169b3a`](https://github.com/sagemath/sagetrac-mirror/commit/8169b3a9c502177e22b852894997d4fc724c7374)**

Reviewer: **David Coudert**

_Issue created by migration from https://trac.sagemath.org/ticket/34797_

