Fix misleading "not found" error when workflow/activity activation fails due to missing DI dependency

[Copilot]

When a registered workflow or activity fails to activate (e.g., a constructor dependency isn't registered in DI), the runtime was swallowing the real exception and reporting WorkflowNotFound/ActivityNotFoundException — pointing developers in completely the wrong direction.

Changes

• IWorkflowsFactory — Added out Exception? activationException to TryCreateWorkflow and TryCreateActivity, enabling callers to distinguish "not registered" (null) from "registered but failed to activate" (exception set)
• WorkflowsFactory — Populates activationException when the factory delegate throws; leaves it null when the name isn't in the registry
• WorkflowWorker — Checks activationException on failure; routes to a distinct error type/message (e.g. System.InvalidOperationException) instead of the generic "not found" path
• Logging.cs — Added LogWorkerWorkflowHandleOrchestratorRequestActivationFailed and LogWorkerWorkflowHandleActivityRequestActivationFailed
• Tests — Updated all callers of TryCreate* for new signature; enhanced existing "factory throws" tests to assert activationException is populated; added new worker-level tests for both workflow and activity activation failure paths

Before: Activity 'SendEmailActivity' not found

After: Activity 'SendEmailActivity' failed to activate: No service for type 'IEmailSender' has been registered.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #1775

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.20%. Comparing base (b3eaad0) to head (9ee7f66).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1781      +/-   ##
==========================================
+ Coverage   61.18%   61.20%   +0.01%     
==========================================
  Files         285      285              
  Lines        8405     8405              
  Branches      974      974              
==========================================
+ Hits         5143     5144       +1     
  Misses       3026     3026              
+ Partials      236      235       -1     

Flag	Coverage Δ
net10.0	61.20% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.