Better GroupBy dunder str/repr/ipython methods

[jdegenstein]

Currently when running in an ipython console:

from build123d import *
nonagon = RegularPolygon(5, 9)
print(str(nonagon.edges().group_by(Axis.X)))
print(repr(nonagon.edges().group_by(Axis.X)))
nonagon.edges().group_by(Axis.X)

Returns a not-so-useful result that doesn't give an idea of the structure of the objects inside:

<build123d.topology.GroupBy object at 0x000002AE7995C850>
<build123d.topology.GroupBy object at 0x000002AE79E3D6D0>
Out[1]: <build123d.topology.GroupBy at 0x2ae77a2c0d0>

This PR changes the behavior to the following by using ipython pretty printing:

[[<build123d.topology.Edge at 0x1e32f0c9c50>],
 [<build123d.topology.Edge at 0x1e32f0cae90>,
  <build123d.topology.Edge at 0x1e32febbb50>],
 [<build123d.topology.Edge at 0x1e32fe00050>,
  <build123d.topology.Edge at 0x1e32febbed0>],
 [<build123d.topology.Edge at 0x1e316c2b310>,
  <build123d.topology.Edge at 0x1e32f101410>],
 [<build123d.topology.Edge at 0x1e32f8612d0>,
  <build123d.topology.Edge at 0x1e315962650>]]
[[<build123d.topology.Edge object at 0x000001E3158BDED0>], [<build123d.topology.Edge object at 0x000001E32F891110>, <build123d.topology.Edge object at 0x000001E32F74BE10>], [<build123d.topology.Edge object at 0x000001E32F101410>, <build123d.topology.Edge object at 0x000001E32F08FED0>], [<build123d.topology.Edge object at 0x000001E316C2B310>, <build123d.topology.Edge object at 0x000001E316B55390>], [<build123d.topology.Edge object at 0x000001E32EC0DC50>, <build123d.topology.Edge object at 0x000001E32F0F0610>]]
Out[1]:
[[<build123d.topology.Edge at 0x1e316b544d0>],
 [<build123d.topology.Edge at 0x1e316c2b310>,
  <build123d.topology.Edge at 0x1e32ec0dc50>],
 [<build123d.topology.Edge at 0x1e30f5aaed0>,
  <build123d.topology.Edge at 0x1e32f0f0610>],
 [<build123d.topology.Edge at 0x1e32f08f550>,
  <build123d.topology.Edge at 0x1e30f610c10>],
 [<build123d.topology.Edge at 0x1e3175e4e90>,
  <build123d.topology.Edge at 0x1e32f0dc050>]]

N.B. in a standard python REPL the return value of the last statement will be equivalent to the second print statement.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (72827ff) 96.24% compared to head (1c61a13) 96.25%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #560   +/-   ##
=======================================
  Coverage   96.24%   96.25%           
=======================================
  Files          24       24           
  Lines        7746     7760   +14     
=======================================
+ Hits         7455     7469   +14     
  Misses        291      291           

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