test: Add retries to tests for engine flakiness

[jtran]

Test flakiness seems to have increased since #1527, and we need to re-run CI jobs more frequently now.

This PR adds retrying in tests. It only retries when errors implement the IsRetryable trait, and that returns true.

When a retryable error occurs, the entire engine connection needs to be scrapped, and everything needs to be redone.

[codecov]

Codecov Report

❌ Patch coverage is 93.37748% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.35%. Comparing base (d038ace) to head (e58a31c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/context.rs	93.15%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1713      +/-   ##
==========================================
+ Coverage   66.28%   67.35%   +1.07%     
==========================================
  Files          44       45       +1     
  Lines        8476     9065     +589     
==========================================
+ Hits         5618     6106     +488     
- Misses       2858     2959     +101     

Flag	Coverage Δ
unittests	67.35% <93.37%> (+1.07%)	⬆️

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