Python: Support informational-only hosted tool calls

[eavanvalkenburg]

Summary

Add first-class Python support for hosted/provider-executed tool calls that should be preserved in transcripts but not executed by Agent Framework function invocation.

Motivation

Some providers return tool-call-like records for tools they already executed or routed to a hosted service, such as OpenAI hosted tools, Anthropic server tools, Gemini server-side tools, and MCP-hosted calls. These should remain visible in conversation history without being treated as local function invocation requests.

Scope

• Add an informational-only flag to function call content.
• Skip informational-only calls in Python function invocation.
• Map hosted/provider-executed tool calls to informational-only content across providers.
• Preserve serialization/round-trip behavior.

Related

Companion issue: #6996.