stream: improve comments regarding end() errors

Cleans up comments and TODOs and tries to provide a
more detail description in regards to error behavior
of end().

PR-URL: https://github.com/nodejs/node/pull/32839


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>