Feature request: Extension attributes for span groups

[svlandeg]

Discussed in #13036

^{Originally posted by sztal October 2, 2023}
Hi!

First, thanks for all the great work at Explosion! I wonder whether there are any plans for implementing the extension attribute mechanism for span groups?

Span groups seem to be opening some very interesting possibilities for modeling text at the level between tokens and sentences, so being able to enhance them with additional methods would be super useful.