chore: remove test_devex.py, update TESTING.md

[Hweinstock]

Issue #, if available: N/A

Description of changes:

Problem

test_devex.py was a non-pytest main() script with no assertions, hardcoded sleeps, Bedrock LLM dependency, and non-test functions (productivity metrics, developer report).

Solution

Delete test_devex.py. Updated TESTING.md to remove the reference.

Testing: Verified coverage via code review of PR 2.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@2afa155). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #325   +/-   ##
=======================================
  Coverage        ?   90.83%           
=======================================
  Files           ?       42           
  Lines           ?     4036           
  Branches        ?      620           
=======================================
  Hits            ?     3666           
  Misses          ?      203           
  Partials        ?      167           

Flag	Coverage Δ
unittests	90.83% <ø> (?)

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