fix: handle allOf with incompatible types

[emmanuel-ferdman]

Description

When an allOf contains sub-schemas with incompatible primitive types (e.g. string + integer), the allof-merge library returns undefined. The code then tries to access .readOnly on that and craches. Fixed by falling back to an empty object {} in both the plugin and theme mergeAllOf wrappers. All call sites already handle empty objects fine.

Motivation and Context

Pages with these kinds of allOf schemas crash on load. This comes up when an API spec overrides a property type through allOf composition, like changing an integer field to a string enum.

Fixes #1231

How Has This Been Tested?

• Added two unit tests for sampleFromSchema with incompatible allOf (top-level and inside a property)
• Added a test endpoint in demo/examples/tests/allOf.yaml

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.

[github-actions]

Visit the preview URL for this PR (updated for commit 3ec416b):

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