Add hergQC docstrings

[MichaelClerx]

Part of #60

• Added docstrings for hergQC module
• Removed unused options in qc2, qc3, and qc5_1
• Made always-used arguments in qc5 and qc6 non-optional
• Removed unused/unnecessary getters and setters in hergQC
• Updated test that was assuming x[0:-1] captures the whole trace (when in fact it misses out the final entry). See Make QCX methods callable stand-alone #97
• Consistent string quotes

[MichaelClerx]

Note that the syntax of these docstrings isn't right, or checked, at the moment, because we haven't set up documentation yet --> this will be fixed in #60 so sticking with imperfect docstrings for now

[joeyshuttleworth]

Looks good! Thanks

[codecov]

Codecov Report

❌ Patch coverage is 89.42308% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.73%. Comparing base (eeb6f11) to head (7300038).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
pcpostprocess/hergQC.py	88.00%	9 Missing ⚠️
tests/test_herg_qc.py	93.10%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   90.52%   91.73%   +1.21%     
==========================================
  Files          11       11              
  Lines         918      871      -47     
==========================================
- Hits          831      799      -32     
+ Misses         87       72      -15     

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