Clean up activity recording

[blink1073]

Avoid deserializing the entire message until we know it is a status message to avoid deserializing large iopub contents.

[codecov-commenter]

Codecov Report

Merging #722 (8abc494) into main (fb25932) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #722   +/-   ##
=======================================
  Coverage   70.94%   70.94%           
=======================================
  Files          62       62           
  Lines        7502     7503    +1     
  Branches     1190     1190           
=======================================
+ Hits         5322     5323    +1     
  Misses       1823     1823           
  Partials      357      357           

Impacted Files	Coverage Δ
jupyter_server/services/kernels/kernelmanager.py	82.59% <100.00%> (+0.05%)	⬆️

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[kevin-bates]

This LGTM Steve, thank you.