Drop python3.13t

[mayeut]

Draft towards #2683 builds on top of #2525 to limit merge issues once/if this comes out of draft.

This PR combines the 3 commits that might be split differently. My preference would be 1st commit (deprecation) then combine the last 2 commits (removal of cp313t and the corresponding enable option). Other possible options I see:

• deprecate only as a pinned issue and combine the deprecation commit/cp313t removal commit, remove the option later.
• deprecate only as a pinned issue and keep this PR as-is
• tell manylinux not to remove cp313t