flush streams and files before/after optimization

[ewu63]

Purpose

The idea is that,

1. we flush stdout and stderr before calling the optimizer, in case prints from the runscript are buffered
2. we flush the output files (which could also be streams) after the end of the optimization, so that stuff printed in the runscript after do not get mixed.

I know we can and should do this for all optimizers, I actually tried to refactor some stuff into "pre-optimization" and "post-optimization" functions shared across all optimizers. But, I stumbled across #402 which means I couldn't actually verify what I was doing with the dummyConstraint was not introducing bugs. We can come back to it after that stuff is all cleaned up.

Expected time until merged

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.33%. Comparing base (4ed7ce9) to head (d38db51).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
pyoptsparse/pySNOPT/pySNOPT.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #403      +/-   ##
==========================================
+ Coverage   74.15%   74.33%   +0.17%     
==========================================
  Files          22       22              
  Lines        3297     3300       +3     
==========================================
+ Hits         2445     2453       +8     
+ Misses        852      847       -5     

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[ewu63]

@sseraj @lamkina

[marcomangano]

LGTM, I will take a look at the other PR, let's talk offline