fix: preserve root component keys in back-references

[goutamadwant]

Pull Request

Description

ResolverCache can resolve an external back-reference from an external component to a component in the original root document. ExternalRefProcessor previously continued into component-name allocation after that lookup. When the root component was itself an external $ref and its declared key differed from the target filename, the allocator treated the root component as a conflict, created a suffixed duplicate, and could mutate the root snapshot. With resolveFully and validateExternalRefs, this later produced an invalid basename-derived lookup.

This PR:

• retains the declared JSON Pointer key when a reference resolves from the root document snapshot
• reuses that key before component allocation and recursive processing for every supported component type
• keeps root-resolved schema targets referenced through component cleanup
• adds the [Bug]: Regression: resolveFully fails when components key does not match external file basename #2399 regression fixture and focused cache, schema-alias, and response tests, including negative fallbacks for absent, nested, and wrong-type pointers

Fixes #2399

Type of Change

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor (non-breaking change)
• 🧪 Tests
• 📝 Documentation
• 🧹 Chore (build or tooling)

Checklist

• I have added/updated tests as needed
• I have added/updated documentation where applicable
• The PR title is descriptive
• The code builds and passes tests locally
• I have linked related issues (if any)

Screenshots / Additional Context

Validated with:

• focused tests for [Bug]: Regression: resolveFully fails when components key does not match external file basename #2399, root-reference caching, root schema-alias retention, external component processing, Duplicated schemas produced when shared schema references local schema #1961, and External Refs with same name are ignored #2055
• the full seven-module mvn --batch-mode package build on Java 11