Start of work on new systematic factory design

[marcpaterno]

Description

Redesign of factories for creation of systematics. This makes the factories more flexible in that the nature of the measurement to which the systematic will be applied partially determines what kind of systematic will be created.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

The following checklist will make sure that you are following the code style and
guidelines of the project as described in the
contributing page.

• I have run bash pre-commit-check and fixed any issues
• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation
• I have 100% test coverage for my changes (please check this after the CI system has verified the coverage)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.0%. Comparing base (4efc44a) to head (54579e6).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #471   +/-   ##
=======================================
  Coverage    99.9%   100.0%           
=======================================
  Files          54       54           
  Lines        4163     4167    +4     
=======================================
+ Hits         4160     4167    +7     
+ Misses          3        0    -3     

Files with missing lines	Coverage Δ
firecrown/ccl_factory.py	100.0% <100.0%> (ø)
firecrown/connector/numcosmo/numcosmo.py	100.0% <100.0%> (+0.2%)	⬆️
firecrown/data_functions.py	100.0% <100.0%> (ø)
firecrown/likelihood/number_counts.py	100.0% <100.0%> (+0.5%)	⬆️
firecrown/likelihood/source.py	100.0% <100.0%> (ø)
firecrown/likelihood/two_point.py	100.0% <100.0%> (+0.4%)	⬆️
firecrown/parameters.py	100.0% <100.0%> (ø)
firecrown/updatable.py	100.0% <100.0%> (ø)