[3.11] gh-105096: Reformat wave documentation (#105136) (#105138) (#105155)

[3.12] gh-105096: Reformat wave documentation (#105136) (#105138)

gh-105096: Reformat wave documentation (#105136)

Add ".. class::" markups in the wave documentation.

* Reformat also wave.py (minor PEP 8 changes).
* Remove redundant "import struct": it's already imported at top
  level.
* Remove wave.rst from .nitignore

(cherry picked from commit 85e5d03163cac106ac8ec142ef03f1349a48948b)
(cherry picked from commit 01b42f9559b614d729c3f055d09269db13d2433c)