Enable proper shallow copying of state mutable sequences

[sdhiscocks]

This gives similar behaviour to a standard list

[codecov]

Codecov Report

Merging #696 (368cc20) into main (ce16944) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #696   +/-   ##
=======================================
  Coverage   94.59%   94.59%           
=======================================
  Files         171      171           
  Lines        8617     8627   +10     
  Branches     1665     1665           
=======================================
+ Hits         8151     8161   +10     
  Misses        341      341           
  Partials      125      125           

Flag	Coverage Δ
integration	69.29% <100.00%> (+0.03%)	⬆️
unittests	92.16% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stonesoup/sensormanager/reward.py	97.67% <ø> (-0.11%)	⬇️
stonesoup/types/state.py	99.43% <100.00%> (+0.01%)	⬆️
stonesoup/types/track.py	100.00% <100.00%> (ø)

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