fix(azure): accept include in provider_options for Responses API models (#990)

* fix(azure): accept include in provider_options for Responses API models

The Azure Responses formatter delegates to the OpenAI Responses encoder,
which already honours `provider_options[:include]` (reasoning signatures,
web_search_call.action.sources, ...). The Azure provider schema never
listed the key, though, and the streaming path validates provider_options
strictly against that schema before the body is built, so any request
that set `include` failed with "unknown options [:include]". The OpenAI
provider has carried the same entry for a while; this adds it to Azure.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J64Gz8aNb6uv6PEfpwgyNr

* Apply suggestion from @vasspilka

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Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>