Start kernel client channels when reusing already running in-process kernel

[dalthviz]

Closes napari/napari#7413

This PR allows multiple napari viewers in the same session to each have a console, with the consoles having linked histories and kernel (active variables).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.51%. Comparing base (c15d804) to head (b526f24).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
+ Coverage   90.38%   94.51%   +4.12%     
==========================================
  Files           4        4              
  Lines         156      164       +8     
==========================================
+ Hits          141      155      +14     
+ Misses         15        9       -6     

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[psobolewskiPhD]

I pulled this down and I can do, in either console:

import numpy as np
data = np.random.random([5, 5])

Then, in either console:

viewer.title     # returns correct title of the viewer with the console
viewer.add_image(data)      #  data is shown in the viewer with the console

But v1 and v2 give NameError: name 'v2' is not defined

this is with this script:

import napari

v1 = napari.Viewer(title="v1")
v2 = napari.Viewer(title="v2")
napari.run()