Add RDataReporting::observables_likelihood

[dweindl]

Add RDataReporting::observables_likelihood for computing observables, likelihood and the respective sensitivities. Closes #2625.

Fixes allocating ReturnData::sllh despite SensitivityMethod::none.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.03%. Comparing base (2d58f54) to head (2168938).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2627      +/-   ##
===========================================
- Coverage    77.05%   77.03%   -0.02%     
===========================================
  Files          332      332              
  Lines        22957    22970      +13     
  Branches      1477     1478       +1     
===========================================
+ Hits         17689    17695       +6     
- Misses        5257     5264       +7     
  Partials        11       11              

Flag	Coverage Δ
cpp	73.96% <100.00%> (-0.02%)	⬇️
cpp_python	33.47% <7.14%> (-0.02%)	⬇️
petab	38.32% <0.00%> (-0.04%)	⬇️
python	72.12% <100.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
include/amici/rdata.h	100.00% <ø> (ø)
src/rdata.cpp	95.60% <100.00%> (+0.09%)	⬆️

... and 2 files with indirect coverage changes