👌 Reset directive option specs at start of build

[ubmarco]

This fixes the problem, that the option_spec attributes are modified on a class level for:

• NeedDirective
• NeedextendDirective
• NeedserviceDirective

and thus remain changed for subsequent sphinx runs in the same interpreter session.

The problem was a finding of #1441.

This is particularly of issue for SN test cases, which all run in the same Python interpreter,
and should ideally be reproducible, independent of any preceding tests run.

The PR defines a reset_options_spec class method for modified directives,
to revert the runtime changes during the config-inited event.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.70%. Comparing base (4e10030) to head (a8c1a38).
Report is 130 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1448      +/-   ##
==========================================
+ Coverage   86.87%   88.70%   +1.82%     
==========================================
  Files          56       62       +6     
  Lines        6532     7332     +800     
==========================================
+ Hits         5675     6504     +829     
+ Misses        857      828      -29     

Flag	Coverage Δ
pytests	88.70% <100.00%> (+1.82%)	⬆️

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[chrisjsewell]

cheers!