Add GIF reader and implement tight plotting for 2D

[akaszynski]

Add a basic GIF reader. This is needed for testing of a separate animation PR.

>>> import pyvista
>>> from pyvista import examples
>>> filename = examples.download_gif_simple(load=False)
>>> filename.split("/")[-1]  # omit the path
'sample.gif'
>>> reader = pyvista.get_reader(filename)
>>> mesh = reader.read()
>>> mesh.plot(rgba=True, zoom='tight', border=True, border_width=2)

[codecov]

Codecov Report

Merging #3038 (c22285f) into main (8887b85) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3038      +/-   ##
==========================================
+ Coverage   94.37%   94.39%   +0.01%     
==========================================
  Files          76       76              
  Lines       16541    16630      +89     
==========================================
+ Hits        15611    15698      +87     
- Misses        930      932       +2     

[MatthewFlamm]

LGTM so far. I had many thoughts on future implementations from this PR, some of which I mentioned here. Feel free to ignore those to keep this PR manageable.

[akaszynski]

LGTM so far. I had many thoughts on future implementations from this PR, some of which I mentioned here. Feel free to ignore those to keep this PR manageable.

Ha! There's only like 10 comments. "Manageable" is sub-300 when GitHub starts breaking down because @adeak found 200 edge cases, typos, and general things I didn't think about. Honestly, I've learned so much about software engineering because you guys are so critical, I appreciate the feedback.

[akaszynski]

@MatthewFlamm, when you get a second, would you mind giving this a quick review?

[MatthewFlamm]

LGTM

[MatthewFlamm]

I like this _GIFReader implementation that mimics the vtk structure better than the PVDReader which I implemented. It gives me some ideas.