fix(cloudformation-diff): classify retained removals as orphaned

[nanookclaw]

Fixes #1882

ResourceDifference.changeImpact currently treats removed resources with DeletionPolicy: RetainExceptOnCreate as WILL_DESTROY. For a resource that already exists and is removed from a template, CloudFormation retains it under this policy, just as it does with Retain.

This changes removal classification to return WILL_ORPHAN for both Retain and RetainExceptOnCreate. Existing no-policy/Delete behavior remains WILL_DESTROY; Snapshot behavior is unchanged, leaving that separate API decision to maintainers.

The existing deletion-impact test is parameterized to cover both retention policies while retaining no-policy coverage.

Validation:

• git diff --check
• Focused Jest test could not run locally: Yarn is not installed, and Corepack could not download the repository's pinned Yarn version because repo.yarnpkg.com was unavailable (EAI_AGAIN).

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[mrgrain]

Nice one, thank you!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.34%. Comparing base (ca8a14a) to head (129f33b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1890      +/-   ##
==========================================
- Coverage   91.38%   91.34%   -0.04%     
==========================================
  Files          80       80              
  Lines       12264    12264              
  Branches     1747     1745       -2     
==========================================
- Hits        11207    11203       -4     
- Misses       1021     1025       +4     
  Partials       36       36              

Flag	Coverage Δ
suite.unit	91.34% <ø> (-0.04%)	⬇️

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