Inset and twin plot

[hanjinliu]

This PR adds more supports of inset/twin plot.

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 81.13%. Comparing base (12b25cd) to head (2bbe8ec).

Files	Patch %	Lines
whitecanvas/types/_tuples.py	42.85%	2 Missing and 2 partials ⚠️
whitecanvas/canvas/_base.py	62.50%	1 Missing and 2 partials ⚠️
whitecanvas/backend/bokeh/canvas.py	96.00%	1 Missing ⚠️
whitecanvas/backend/pyqtgraph/_base.py	96.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #34      +/-   ##
==========================================
+ Coverage   81.11%   81.13%   +0.02%     
==========================================
  Files         162      162              
  Lines       18026    18089      +63     
  Branches     3104     3114      +10     
==========================================
+ Hits        14622    14677      +55     
- Misses       2612     2616       +4     
- Partials      792      796       +4     

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