Windows: add guards for some methods that don't work/exist on windows

[Tom-Willemsen]

This PR contains some minimal changes to allow a FastCS driver to start on Windows.

• loop.add_signal_handler() is not available on windows. On windows, signals are always delivered to the main thread of an application. Ctrl-c does correctly stop a FastCS driver in non-interactive mode on windows without this handler.
• StdoutProxy didn't work on windows under pytest - I believe it is conflicting with pytest's stdout capturing. Just use sys.stdout for that case.

FastCS' own unit tests don't pass on Windows even with this change - that would require a larger PR.

[codecov]

Codecov Report

❌ Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.67%. Comparing base (c86f760) to head (470cf55).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fastcs/logging/_logging.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #295      +/-   ##
==========================================
- Coverage   90.82%   90.67%   -0.15%     
==========================================
  Files          70       70              
  Lines        2486     2532      +46     
==========================================
+ Hits         2258     2296      +38     
- Misses        228      236       +8     

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[GDYendell]

This looks good. Just a couple of minor changes.

[GDYendell]

Thanks @Tom-Willemsen !