Annotations extras

[PierreGtch]

• closes container for eye tracking related annotation information #12208
• closes [WIP [ENH] metadata attribute for Annotations #12213

Reference issue (if any)

This PR replaces #13213

What does this implement/fix?

The difference with #13213 is that the additional information is a list[dict[str, str | int | float | None]] instead of a dataframe

[PierreGtch]

@drammock I implemented here the recommendations in your #13213 (comment)

[drammock]

just a quick first pass with some high-level stuff, LMK when I should take another look @PierreGtch

[agramfort]

I am onboard with the change although I am not convinced about the word "details"

[drammock]

I think this is close. I've left several questions below. One thing I want to make sure of (but ran out of time to check) is that users can modify extras in-place (the way they can with onset, duration, etc). In other words:

annotations.onset[3] = 7.1  # this works
annotations.extras[3] = dict(reaction_time=0.7)  # this should be possible
annotations.extras[3].update(dict(button="left"))  # this also should be possible

[PierreGtch]

@drammock I addressed your comments but left some questions. In particular:

annotations.extras[3].update(dict(button="left"))  # this also should be possible

This is possible and the type of the new extras will be checked

annotations.extras[3] = dict(reaction_time=0.7)  # this should be possible

This is also possible but the type of the new extras will NOT be checked. You think this would be an issue?
To enforce it, a possibility would be to also write a custom list class which would overwrite __setitem__ to replace the input dict with an _AnnotationsExtraDict

Feel free to merge if you are satisfied with the current state :)

[drammock]

This is also possible but the type of the new extras will NOT be checked. You think this would be an issue?

I think this may be the more common use case (it more closely mirrors what users currently do with the description field for example). A custom subclass of list is indeed probably the right way to solve it; I'm doing something very similar here:

https://github.com/mne-tools/mne-python/pull/13059/files#diff-8958de0220265a954fac8d4e75521b1917748cdd5e15ce759b5e627b1d401b7cR779-R783

[PierreGtch]

All good @drammock :)