Selection manager

[hanjinliu]

This PR implements a ImageJ-like interface for manual selection management.

[codecov]

Codecov Report

Attention: Patch coverage is 55.59441% with 127 lines in your changes missing coverage. Please review.

Project coverage is 83.51%. Comparing base (164674a) to head (89ac325).

Files with missing lines	Patch %	Lines
whitecanvas/tools/_selection.py	45.11%	118 Missing ⚠️
whitecanvas/tools/_selection_types.py	88.23%	4 Missing and 4 partials ⚠️
whitecanvas/types/_tuples.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
- Coverage   83.85%   83.51%   -0.34%     
==========================================
  Files         198      199       +1     
  Lines       22266    22479     +213     
  Branches     3679     3721      +42     
==========================================
+ Hits        18671    18774     +103     
- Misses       2642     2753     +111     
+ Partials      953      952       -1     

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