refactor: make ParticleDynamics mutable

[redeboer]

Allows one to set a custom Dynamics class for a particle, as long as it derives from Dynamics.

Closes #424

[codecov]

Codecov Report

Merging #434 (9d919d3) into master (38e575d) will decrease coverage by 0.01%.
The diff coverage is 80.70%.

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
- Coverage   90.02%   90.00%   -0.02%     
==========================================
  Files          22       22              
  Lines        3437     3462      +25     
  Branches      847      854       +7     
==========================================
+ Hits         3094     3116      +22     
- Misses        173      175       +2     
- Partials      170      171       +1     

Flag	Coverage Δ
unittests	90.00% <80.70%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
src/expertsystem/io/_dict/build.py	84.05% <78.57%> (-0.82%)	⬇️
src/expertsystem/amplitude/model.py	91.70% <82.75%> (-1.13%)	⬇️
src/expertsystem/reaction/conservation_rules.py	92.15% <0.00%> (+0.58%)	⬆️
src/expertsystem/io/_dict/dump.py	83.83% <0.00%> (+2.02%)	⬆️