fix(resolver): resolve nested external array item $refs - #11067

Description

Fixes resolver failures for $refs that point at array items schemas living in nested external OpenAPI documents (PathItem → external schema → array items $ref). Isolation of the strict-retry cache avoids unrelated cache eviction while still clearing failed resolutions.

Motivation and Context

Fixes #11018

How Has This Been Tested?

• Added Cypress multi-file regression fixture under test/e2e-cypress/static/documents/bugs/11018/ and test/e2e-cypress/e2e/bugs/11018.cy.js
• Targeted Cypress pass; related allOf Cypress pass
• 866 unit tests pass; artifacts and build pass; targeted lint pass
• Full repo lint still reports two unrelated pre-existing errors

Screenshots (if appropriate):

N/A

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.