Fix Shield protection orphaning when deleting ALBs during ingress teardown

[ShiriNmi1520]

Issue

Fixes #4042

Description

This PR fixes orphaned AWS Shield protections when an ALB is deleted during a full Ingress teardown.

Key changes:

• Added Shield cleanup in the ALB deletion path in load_balancer_synthesizer:
  • Before deleting an unmatched ALB, the controller now checks for existing Shield protection and deletes it if it is controller-managed.
  • Cleanup is limited to ALBs and only runs when Shield reconciliation is enabled/subscribed.
• Kept ownership safety:
  • Unmanaged Shield protections are detected and intentionally not deleted.
• Refactored Shield subscription gating:
  • stack_deployer now computes shieldReconcileEnabled once and uses it for both Shield synthesiser registration and ALB delete-time cleanup.
• Reused managed-name logic:
  • Introduced/reused IsManagedProtectionName in Shield synth code to keep behaviour consistent.
• Added regression tests:
  • New tests cover ALB teardown, cleanup flow and error/guardrail cases (cleanup disabled, non-ALB, unmanaged protection, API errors).

Manual validation:
Executed make test.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

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• ✅ login: ShiriNmi1520 / name: Yuutetsu (0949f3d, 3dea548, 741db0c)

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