fix complex awk parsing bug in command_variables [AI]

[rfbgo]

I was initially suspicious this was truly functionally equivalent. After some back and forth with gemini I now think it's ready for review.

[gemini-code-assist]

Code Review

This pull request simplifies command execution in CommandVariable.extract_value by replacing manual command parsing and piping logic with subprocess.Popen(..., shell=True). It also adds a new test suite to verify pipeline escaping, logical chaining, and stderr redirection. The review feedback suggests handling potential UnicodeDecodeError exceptions by using errors="replace" when decoding stdout and stderr.

[ramble-pr-bot]

Ramble Performance Test Metrics

Results produced with commit: c0b51a1

Test Name	Outcome	Duration (s)	Most Recent Run (s)	Last 5 Avg (s)
test_analyze_large_file	passed	3.0016	2.1238 (09e1067)	2.6568
test_large_template_expansion	passed	2.0599	1.5451 (09e1067)	1.8747
test_many_experiments	passed	33.3271	28.2463 (09e1067)	31.6371
test_many_objects_defaults	passed	20.9729	16.4979 (09e1067)	19.1804
test_matrix_filter_perf	passed	1.2722	1.0270 (09e1067)	1.1809

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.44%. Comparing base (ff2e049) to head (c0b51a1).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1690      +/-   ##
===========================================
+ Coverage    93.37%   93.44%   +0.07%     
===========================================
  Files          368      369       +1     
  Lines        35570    35610      +40     
===========================================
+ Hits         33214    33277      +63     
+ Misses        2356     2333      -23     

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