First Pass Documentation (docstrings) For Observation Folder

[AFg6K7h4fhy2]

This pull request includes a first pass for:

• Correction and or modifications of existing docstrings in ./model/src/pyrenew/observation
• Addition of new docstrings in ./model/src/pyrenew/observation

Find other relevant PRs here (74 and 73)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.49%. Comparing base (06e8a22) to head (c87804c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
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  Coverage   90.49%   90.49%           
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  Files          28       28           
  Lines         547      547           
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  Hits          495      495           
  Misses         52       52           

Flag	Coverage Δ
unittests	90.49% <100.00%> (ø)

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