Add the ability to have a slicing plane for one structure only

[Thibaulltt]

I end up uploading tons of structures grouped into groups to polyscope at once, and analyze them later. When I want to hide a certain part of one structure, I can create a slicing plane and manually disable its effect on all structures I want to see whole, but this is time-consuming.

This PR adds the ability to add a slicing plane for one structure only, through that structure's Options > Slice planes menu in the Structures window. It does not change anything about the "global" slicing plane controls in View > Slice Planes.

Additionally, the buttons to add slice planes (both globally and per-structure) are now always visible in that structure's menu. I can thus quickly add structure-specific slicing planes at will even when some are already enabled.

[Thibaulltt]

As with my other PR, this is directly available to the polyscope-py library if its dependency to polyscope is bumped :)

[Thibaulltt]

Edit: by trying to have "fancy names" for the slicing planes (Slice plane of <structure name>), it ends up being more complicated/stateful with no real benefit. 9f340c1 removes the supplied name to addSlicePlane().

[nmwsharp]

I think this is a good change, I'm happy to merge it. I see some traffic on the PR here, let me know when it is good to go on your end.

[Thibaulltt]

Let me ponder on it 'till Friday!

[Thibaulltt]

I noticed MSVC does not define the 'and' and 'or' operators unless some compiler flags are enabled [1] (which is why the windows build fails). I have a patch ready for it, I'll send it on Friday if I don't find anything more in the meantime, to avoid restarting a full CI run :)

[1]: https://learn.microsoft.com/en-us/cpp/cpp/keywords-cpp?view=msvc-170 , note (b)