gh-62040: Raise ValueError on invalid *errors* argument in several codecs

[StanFromIreland]

• Issue: codecs use assert for runtime validity checks #62040

[efimov-mikhail]

I can see that there's only some changes from last patch:
https://bugs.python.org/file30902/issue17840.patch

For example, I'd like to remove also assert self.errors == 'strict', use _check_strict method in all files, test new changes.

[StanFromIreland]

Ah I forgot about the patch and my grep was too strict, I'll fix all the self.errors cases.