Make periodic callback counter a parameter

[philippjfr]

Fixes #4125

[codecov]

Codecov Report

Merging #4134 (9a3cb6e) into master (ebd7fc5) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4134      +/-   ##
==========================================
- Coverage   83.56%   83.48%   -0.08%     
==========================================
  Files         224      224              
  Lines       33381    33367      -14     
==========================================
- Hits        27895    27857      -38     
- Misses       5486     5510      +24     

Flag	Coverage Δ
ui-tests	37.55% <100.00%> (-0.07%)	⬇️
unitexamples-tests	74.54% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
panel/io/callbacks.py	79.85% <100.00%> (+1.01%)	⬆️
panel/tests/ui/io/test_jupyter_server_extension.py	50.00% <0.00%> (-50.00%)	⬇️
panel/tests/ui/io/test_jupyterlite.py	89.18% <0.00%> (-8.11%)	⬇️
panel/tests/pane/test_vtk.py	87.82% <0.00%> (-5.17%)	⬇️
panel/tests/ui/io/test_convert.py	92.92% <0.00%> (-2.66%)	⬇️
panel/tests/command/test_serve.py	83.95% <0.00%> (-1.42%)	⬇️
panel/tests/util.py	87.25% <0.00%> (-1.10%)	⬇️
panel/tests/conftest.py	87.50% <0.00%> (-0.92%)	⬇️
panel/pane/vtk/synchronizable_serializer.py	77.35% <0.00%> (-0.32%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
... and 7 more

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