Creating constructiors for ready objects.

[marcpaterno]

This PR will be a step towards one-phase construction of Statistics and contained objects. This will eventually allow us to remove the read step, and thus simplify the construction of likelihoods.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.8%. Comparing base (221cf65) to head (bcd54a5).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #399     +/-   ##
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+ Coverage    95.5%   97.8%   +2.3%     
========================================
  Files          34      35      +1     
  Lines        2569    2989    +420     
========================================
+ Hits         2454    2926    +472     
+ Misses        115      63     -52     

Files	Coverage Δ
firecrown/connector/cosmosis/likelihood.py	97.0% <100.0%> (+5.0%)	⬆️
...ood/gauss_family/statistic/source/number_counts.py	83.8% <100.0%> (+5.1%)	⬆️
...likelihood/gauss_family/statistic/source/source.py	100.0% <ø> (ø)
...hood/gauss_family/statistic/source/weak_lensing.py	92.7% <100.0%> (+7.5%)	⬆️
...own/likelihood/gauss_family/statistic/two_point.py	96.8% <100.0%> (+20.6%)	⬆️
firecrown/metadata/two_point.py	100.0% <100.0%> (ø)
firecrown/utils.py	100.0% <100.0%> (ø)