feat: extract intensity components

[redeboer]

Closes #184

[redeboer]

@spflueger Currently, the functions are only implemented in usage/step3 notebook. We have to think where and how this can be integrated into the package.
https://pwa--244.org.readthedocs.build/projects/tensorwaves/en/244/usage/step3.html#intensity-components

[codecov]

Codecov Report

Merging #244 (e08f084) into master (eba05ac) will decrease coverage by 0.49%.
The diff coverage is 64.00%.

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   79.31%   78.81%   -0.50%     
==========================================
  Files          12       13       +1     
  Lines         585      609      +24     
  Branches       79       89      +10     
==========================================
+ Hits          464      480      +16     
- Misses         90       95       +5     
- Partials       31       34       +3     

Flag	Coverage Δ
unittests	78.81% <64.00%> (-0.50%)	⬇️

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

Impacted Files	Coverage Δ
src/tensorwaves/model.py	53.42% <50.00%> (+0.64%)	⬆️
src/tensorwaves/physics.py	65.21% <65.21%> (ø)