refactor: split scenario instantiation helpers

[Brad-Edwards]

Summary

• move instantiated-scenario validation helpers into a focused internal module
• reduce aces_sdl/scenario.py from 501 lines to 469 lines
• preserve the existing scenario models and validation behavior

Root cause

PR #808 fails SonarCloud rule python:S104 because implementations/python/packages/aces_sdl/scenario.py exceeds the configured 500-line limit by one line.

Impact

This is an internal refactor with no public API, schema, or runtime behavior change. Once merged into dev, PR #808 will receive the fix on its head branch and SonarCloud can re-evaluate the quality gate.

Requirement context

• Requirement UID: DSL-435
• Ground Control project: aces-sdl

Validation

• 63 passed in focused instantiated-scenario and phase-contract tests
• canonical tools/verify_all.py passed
• 3,882 passed, 1 skipped, 46 deselected; aggregate coverage 92%
• 34 passed, 2 environment-gated skips in integration tests
• repository policy, requirement-governance, schema, lineage, lint, secret scanning, and documentation gates passed

The requirement-governance HTTP client timed out against gc-dev; the repository checker recorded its configured service-unavailable skip. The corresponding DSL-435 traceability link for the new internal module was created successfully through Ground Control.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud