Simplify locations where the OS and env are accessible

[Baptouuuu]

They're now only accessible when building services. The goal is to force the use of services, otherwise too much logic can be put in the framework configuration (thus reducing testability).

Yet people can set the OS and environment as services and access them like before with little extra work.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (61f295e) to head (552738a).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #15      +/-   ##
=============================================
- Coverage      94.54%   94.50%   -0.04%     
  Complexity       110      110              
=============================================
  Files             13       13              
  Lines           1374     1365       -9     
=============================================
- Hits            1299     1290       -9     
  Misses            75       75              

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