Move ModelState and ModelDimension classes to separate files

[dweindl]

... because thousands of line per file are a pain

(Only moving code, no further changes)

[codecov]

Codecov Report

Merging #1416 (d10f9fb) into develop (e657f37) will decrease coverage by 0.02%.
The diff coverage is 77.77%.

@@             Coverage Diff             @@
##           develop    #1416      +/-   ##
===========================================
- Coverage    78.77%   78.74%   -0.03%     
===========================================
  Files           65       66       +1     
  Lines        10061    10061              
===========================================
- Hits          7926     7923       -3     
- Misses        2135     2138       +3     

Flag	Coverage Δ
cpp	75.31% <77.77%> (-0.05%)	⬇️
petab	69.48% <ø> (ø)
python	67.72% <ø> (ø)

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

Impacted Files	Coverage Δ
include/amici/model.h	66.66% <ø> (-4.17%)	⬇️
src/model_state.cpp	77.77% <77.77%> (ø)
src/exception.cpp	82.60% <0.00%> (-8.70%)	⬇️
src/solver_cvodes.cpp	70.20% <0.00%> (-0.21%)	⬇️

[sonarcloud]

SonarCloud Quality Gate failed.

0 Bugs
0 Vulnerabilities
0 Security Hotspots
3 Code Smells

0.0% Coverage
0.0% Duplication