BUG: Some raw classes use attributes rather than ._raw_extras

[larsoner]

Extra [attributes] are not supposed to be part of the RawEyelink class. You need to put it all in _raw_extras[0]. This can be a dict, too. This is going to be a big change so you don't need to do it here -- we can figure it out later. I'll create a new issue about adding a test for this since it's possible there are other readers that need to be updated, too.

Originally posted by @larsoner in #11823 (comment)

I propose we add a test to _test_raw_reader that there aren't extra attributes added to the class other than what's expected based on BaseRaw. In principle maybe this should involve an ABC and some automated checking, but to KISS I might start by manually coding a test in _test_raw_reader. I don't expect it to be more than a dozen lines or so.