Add workflow state rehydration diagnostics

[sfmskywalker]

Summary

• log structured warnings when workflow-state rehydration cannot resolve an activity execution context
• log structured warnings when completion callback owners or child nodes cannot be resolved
• classify skips as migration-compatible or unexpected by comparing persisted and target definition version IDs
• include workflow, definition, context, owner, and child identifiers for querying and alerting

Root cause

WorkflowStateExtractor intentionally skipped unresolved references to preserve workflow migration compatibility, but those paths emitted no diagnostics. The same silent behavior also concealed stale or inconsistent same-version state.

Impact

Existing skip behavior remains unchanged, including intentional migration scenarios. Operators now receive structured warnings that distinguish expected migration cleanup from potentially inconsistent persisted state.

Validation

• dotnet test test/unit/Elsa.Workflows.Core.UnitTests/Elsa.Workflows.Core.UnitTests.csproj --no-restore — 202 passed
• dotnet build src/modules/Elsa.Workflows.Core/Elsa.Workflows.Core.csproj --no-restore — succeeded for net8.0, net9.0, and net10.0 with 0 warnings/errors
• git diff --check

Fixes #7772