Overhauled redirection and output capturing

[kmvanbrunt]

cmd2 redirection now only captures output directed to self.stdout (e.g., via self.poutput()). Standard print() calls write directly to sys.stdout and are not captured. However, print() calls within pyscripts and the interactive Python shell are treated as command output and sent to self.stdout, allowing them to be captured.

This means we no longer alter the system-wide sys.stdout stream.

To facilitate this change, our custom argparse code now writes all output to self.stdout instead of sys.stdout.

To support pyscript developers who don't have access to self.stdout, the print() function in that environment has been replaced with one that wraps self.print_to(). It writes to self.stdout by default and respects the allow_style setting. It also supports printing Rich objects. This means that run_pyscript script.py > out.txt will capture any print() calls in the script.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.49%. Comparing base (a3890a7) to head (770b819).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1654      +/-   ##
==========================================
- Coverage   99.49%   99.49%   -0.01%     
==========================================
  Files          21       21              
  Lines        4741     4733       -8     
==========================================
- Hits         4717     4709       -8     
  Misses         24       24              

Flag	Coverage Δ
unittests	99.49% <100.00%> (-0.01%)	⬇️

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