Added metric factory

[eacharles]

Problem & Solution Description (including issue #)

Added MetricFactory and associated tests.

Also, added interface functions to src/qp/metrics/init.py

Code Quality

• My code follows the code style of this project
• I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3fec754) 99.96% compared to head (e489b3b) 99.96%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #209   +/-   ##
=======================================
  Coverage   99.96%   99.96%           
=======================================
  Files          36       37    +1     
  Lines        2529     2569   +40     
=======================================
+ Hits         2528     2568   +40     
  Misses          1        1           

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[drewoldag]

🤦 <- I'm glad there's a facepalm emoji in slack.

[drewoldag]

This all looks fine to me. Thanks for putting this together.