feat: implement FitResult.count_number_of_parameters

[redeboer]

Closes #290

• Added a method FitResult.count_number_of_parameters()
• Constructor arguments of FitResult are now validated. This is to ensure that functions and methods like count_number_of_parameters() keep working.
• All parameters in FitResult are now 'pretty printed' below each other, e.g.:

  FitResult(
   minimum_valid=True,
   execution_time=2.9841978549957275,
   function_calls=166,
   estimator_value=-7579.247627538372,
   parameter_values={
    'm_f(0)(980)': 0.989885368944097,
    'Gamma_f(0)(980)': 0.060228379644260165,
   },
   parameter_errors={
    'm_f(0)(980)': 0.0010628340144144574,
    'Gamma_f(0)(980)': 0.0016523232241513362,
   },
  )

• AIC and BIC example provided in documentation.
• Using type alias ParameterValue where possible instead of Union[...].

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[redeboer]

@Leongrim, hope you agree with #290 (comment), that this PR serves as a sufficient solution to #290. For AIC and BIC, see changes to step 3.

[codecov]

Codecov Report

Merging #291 (2c60e8f) into main (272a9b7) will decrease coverage by 0.70%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
- Coverage   81.25%   80.54%   -0.71%     
==========================================
  Files          13       13              
  Lines         816      843      +27     
==========================================
+ Hits          663      679      +16     
- Misses        153      164      +11     

Flag	Coverage Δ
unittests	80.54% <76.92%> (-0.71%)	⬇️

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

Impacted Files	Coverage Δ
src/tensorwaves/interfaces.py	76.14% <65.71%> (-6.00%)	⬇️
src/tensorwaves/estimator.py	73.33% <100.00%> (ø)
src/tensorwaves/model.py	72.27% <100.00%> (ø)
src/tensorwaves/optimizer/_parameter.py	100.00% <100.00%> (ø)
src/tensorwaves/optimizer/callbacks.py	75.00% <100.00%> (+0.13%)	⬆️
src/tensorwaves/optimizer/minuit.py	93.22% <100.00%> (ø)
src/tensorwaves/optimizer/scipy.py	93.10% <100.00%> (ø)