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.

[efimov-mikhail]

Maybe _check_strict from the original patch would be better?

[StanFromIreland]

I prefer assert_strict since it is closer to what was there before, and it is more obvious, to me at least, that it will fail if errors != 'strict', whereas check_strict, seems like something that will enable more verbose errors or the like.

[efimov-mikhail]

IMO, it's not fully correct to name method assert_something and don't make any assert checks or raising an AssertionError.

[StanFromIreland]

@malemburg which do you prefer? _check_strict or _assert_strict

[StanFromIreland]

Friendly ping @malemburg