[codex] Share fake data context

[k-kinzal]

What changed

• Added FakeDataContext to hold one schema, one OperationLookup, one configured OpenAPIFaker, and the resolved faker options.
• Updated Interceptor to create a single fake-data context and reuse it for operation lookup and generated responses.
• Updated FakeRequest and FakeResponse to accept FakeDataContext as a source and to route lookup/faker calls through the context.
• Documented FakeDataContext as a reusable source for standalone generation.

Why

Operation lookup and OpenAPI faker creation were repeated across Interceptor, FakeRequest, and FakeResponse. This scattered the generation setup and forced hot request paths to rebuild faker state for every generated response.

Impact

Existing Server and Schema sources continue to work. Callers that generate multiple requests/responses from the same schema can now create one FakeDataContext and reuse it.

Validation

• composer test
• composer lint