Fix loaded relation index lookups in StoredWorkflow

[rmcdaniel]

Summary

Replace firstWhere('index', ...) lookups on loaded logs and timers relations with direct raw-attribute checks.

Prevent replay paths from ever treating index like an Eloquent relation/method, which matches the reported StoredWorkflowLog::index() failure.

Add regression coverage to ensure loaded relation lookups do not fall back to firstWhere() again.

Why

The reported crash happens while replaying workflow state for child/activity stubs. The stack trace points at findLogByIndex(), and the risky part was the in-memory lookup against an already-loaded Eloquent collection. This change hardens that path and the equivalent timer lookup as well.

I couldn’t reproduce the exact exception but this fixes the code path implicated by the report and adds tests to keep it from regressing.

Fixes #360

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1785f13) to head (d9d19d9).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #361   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       577       579    +2     
===========================================
  Files             62        62           
  Lines           2003      2007    +4     
===========================================
+ Hits            2003      2007    +4     

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