Allow configuring context around `fold`ed code

[epage]

#109 fixed an inconsistency in how we folded code before and after all of the annotations.

Callers would likely want to control how much context is shown around each annotation.

[chengr4]

Hi @epage,

I’m also working on addressing this ticket and would appreciate your guidance again lol.

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My imagination is to create a new function eg show_context(num: u8) which works when snippet.fold == false for Snippet.

ps. in the function, counting Max context line for each annotation is needed.

[epage]

It'd likely be best for us to hold off on an issue like this until we have people who specifically need it so we can gather requirements rather than trying to guess what users need.