fix: animations

[romgrk]

A few things happening here:

• Some refactoring:
  • Split render.update(...) in two, extract tabs calculation
  • Move out impure side-effects
  • Rename some fields, mainly real_... to computed_...
• Fix the open & close animation
• Increase the animation frequency, make it feel smoother

@Iron-E This might conflict with some of your changes but I'd rather we merge this first, these changes will help us maintain the plugin better.

[romgrk]

@Iron-E @tobealive I have reverted some of the offset truncation changes, they were causing issues and I didn't want to debug here.

Regarding the changes, I also think they weren't optimal, the groups functions are meant to be as pure as possible, we shouldn't add render-specific logic in them, they're here to slice stuff that has already been computed. If we want to add an ellipsis, it should be computed at the layout phase.

A good next refactoring step could be to extract all of them into lua/barbar/groups.lua.

[Iron-E]

68 might be a good replacement for the ellipsis functionality anyway

[ttytm]

I have reverted some of the offset truncation changes, they were causing issues and I didn't want to debug here.

Thanks for the info @romgrk! Should have checked better that this isn't just handling the sidebar offset. But this re-introduced a shifted offset on truncation. Should there be some separate handling of the sidebar offset truncation or will #68 tackle this as well? Let me know if I can help out somehow.

[romgrk]

We should add the truncation logic again, but it should be handled outside of slice_groups_right, which is too low-level for this kind of logic.