Document reader parser-level exceptions

[Copilot]

Pull Request

Description

Clarifies reader behavior when input is invalid before OpenAPI parsing begins. ReadResult.Diagnostic covers OpenAPI semantic errors; JSON/YAML syntax-level failures may throw before a result can be created.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Related Issue(s)

Linked by automation.

Changes Made

• Added XML remarks to IOpenApiReader read and fragment APIs.
• Documented JSON/YAML parser-level exception behavior on concrete reader entry points.
• Propagated the same contract to OpenApiModelFactory and OpenApiDocument convenience APIs.

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Versions applicability

• My change applies to the version 1.X of the library, if so PR link:
• My change applies to the version 2.X of the library, if so PR link:
• My change applies to the version 3.X of the library, if so PR link:
• I have evaluated the applicability of my change against the other versions above.

See the contributing guidelines for more information about how patches are applied across multiple versions.

Additional Notes

Documentation-only change; no runtime behavior changes.

• Fixes OpenApiYamlReader.Read inconsistent behavior for errors #3056