Do not use assert for input validation in the base64 module

[serhiy-storchaka]

Bug report

Some functions in the base64 module used assert to check parameters. This is a bad practice, because in best case you will get different exceptions for invalid parameter values depending on the -O level. In worst case you can get incorrect result.

Most of such asserts were recently removed, but the one in base64.b32encode() was left.

This behavior was documented, so we do not need to backport the change.

Linked PRs

• gh-148153: Do not use assert for parameter validation in base64 #148154

[serhiy-storchaka]

Actually, it was documented for altchars, not map01. Anyway, I am not sure that it is worth to backport this change. Such error should never occur in production code, so the type of exception does not matter much.