Add --stressor flag to run a single memory stressor (New)

[mreed8855]

Add a --stressor NAME option that runs just the named memory
stressor using the timeout and thread-count rules of the list it
belongs to, and errors out for unknown names.

Description

• At times it is necessary to run a single stress-ng memory stress stressor for debugging purposes. Rather than editing the code each time I created this patch.
• I created a patch to run an individual memory stressor

Resolved issues

Documentation

Tests

[codecov]

Codecov Report

❌ Patch coverage is 5.26316% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.90%. Comparing base (fe4a50c) to head (956c66a).

Files with missing lines	Patch %	Lines
providers/base/bin/stress_ng_test.py	5.26%	17 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2526      +/-   ##
==========================================
- Coverage   58.92%   58.90%   -0.03%     
==========================================
  Files         476      476              
  Lines       48039    48058      +19     
  Branches     8577     8582       +5     
==========================================
+ Hits        28306    28307       +1     
- Misses      18837    18857      +20     
+ Partials      896      894       -2     

Flag	Coverage Δ
provider-base	34.07% <5.26%> (-0.04%)	⬇️

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