Rewrite CRDB pool retry tests to use synctest

[ivanauth]

Summary

Rewrites the CRDB pool retry tests to use Go's testing/synctest package for better time simulation and test reliability.

Fixes #2713

Changes

• Wrap all retry tests in synctest.Test(t, func(t *testing.T) { ... })
• Use t.Context() instead of context.Background()
• Add t.Parallel() for concurrent test execution

Benefits

• Tests no longer rely on real time delays
• More deterministic test execution
• Faster test runs with simulated time
• Better parallel execution support

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.73%. Comparing base (ae83447) to head (e65d882).
⚠️ Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2754      +/-   ##
==========================================
+ Coverage   77.03%   77.73%   +0.70%     
==========================================
  Files         466      473       +7     
  Lines       49199    49906     +707     
==========================================
+ Hits        37896    38787     +891     
+ Misses       8514     8255     -259     
- Partials     2789     2864      +75     

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