gh-95975: Move except/*/finally ref labels to more precise locations (#95976)

* gh-95975: Move except/*/finally ref labels to more precise locations

* Add section headers to fix :keyword: role and aid navigation

* Move see also to the introduction rather than a particular subsection

* Fix other minor Sphinx syntax issues with except

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>

* Suppress redundant link to same section for except too

* Don't link try/except/else/finally keywords if in the same section

* Format try/except/finally as keywords in modified sections

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>