Revert "fix: remove unused WorkflowEvent import and restore 'invalid content' retry check"

[Roopan-Microsoft]

Reverts #275

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	3097	208	93%

report-only-changed-files is enabled. No files were changed during this commit :)

Tests	Skipped	Failures	Errors	Time
588	0 💤	0 ❌	0 🔥	19.318s ⏱️

[github-actions]

Processor Coverage Report •

File	Stmts	Miss	Cover	Missing
src/processor/src/libs/agent_framework
azure_openai_response_retry.py	369	139	62%	193, 201, 223, 249, 259–261, 385, 392–395, 397–399, 405–407, 424, 445–446, 451–454, 457–460, 462–465, 467, 477–479, 481–484, 486–489, 491–495, 497, 505–507, 509, 532–537, 539–541, 547–548, 552–555, 559, 562, 570–571, 577–578, 583, 585, 606, 612–614, 618–619, 635–636, 638–641, 645, 648, 656–657, 663–665, 667–670, 672–683, 686, 693–694, 719–720, 727–728, 730, 734, 737–738, 742–743, 745–747, 755, 757–759, 761–763, 765–766, 776
src/processor/src/steps
migration_processor.py	264	40	84%	88–89, 145–146, 160, 187, 222–223, 229–230, 234, 238, 309–312, 315–318, 322–323, 336–337, 395–396, 496–497, 547–548, 555–556, 594–595, 613–614, 678–679, 703, 732
TOTAL	5750	735	87%

Tests	Skipped	Failures	Errors	Time
812	0 💤	0 ❌	0 🔥	19.815s ⏱️

[github-actions]

🎉 This PR is included in version 2.1.1 🎉

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