fix(http): honor schema examples on anyOf static mocks

[breken-ai]

Addresses #2726

Summary

Prism's static sampler walks into anyOf and oneOf before reading examples on the enclosing schema. Promote the first such example to example on a cloned schema before sampling. This leaves the caller's schema and existing example payloads unchanged and preserves current behavior for schemas without unions.

Checklist

• I tested these changes manually in my local or dev environment. The issue schema now produces {"title":"Some kind of title"} through the static HttpMocker path.
• Tests: Added or updated. HttpMocker.spec.ts fails on base 2426fc0900717a9039b23fc901885239871143fe ("string" returned) and passes with this change (29 tests, 2 snapshots).
• Event Tracking: N/A; this change adds no event tracking.
• Error Reporting: N/A; this change does not change error reporting.