[RFC] Exempt input type and value validation from BC Break policy

Hi all,

Thanks for the RFC. I have a real‑world example that seems to fit this
“input validation” category and wanted to sanity‑check it with you.

I opened PR #21319 to promote a few ext/snmp invalid‑input warnings to
ValueError (only for invalid inputs). Valid inputs behave the same; the
goal is just to make errors catchable and consistent with other extensions.

If this RFC passes, would a change like that be OK without a separate
per‑function RFC? And are there any expectations you’d want contributors to
follow (tests, deprecation note, minor vs major timing)?

Happy to share more details if needed.

Thanks,
Pratik