Python: add Xquik function tool sample

[kriptoburak]

Motivation and Context

Fixes #5792.

This adds a concrete Python function-tool sample for API-key backed external research tools. It keeps Xquik write actions out of scope and uses local sample data when XQUIK_API_KEY is not set, so normal sample validation does not need new Xquik secrets.

Description

• Adds xquik_function_tools.py under python/samples/02-agents/tools/.
• Defines async @tool functions for Xquik read endpoints: post search, user lookup, user posts, and trends.
• Uses FoundryChatClient with AzureCliCredential, matching the current default sample guidance.
• Uses Python standard-library HTTP utilities, so the sample does not add dependencies.
• Adds a tools folder README and documents the Xquik sample setup.

Focused validation run locally:

• Ruff format and check for the new sample passed.
• poe syntax sample check passed.
• Targeted Pyright for xquik_function_tools.py passed.
• Imported the sample with XQUIK_API_KEY empty and verified the Xquik tools return sample_data.
• Repository-wide sample Pyright currently fails on unrelated existing 04-hosting/foundry-hosted-agents imports for agent_framework_foundry_hosting and azure.ai.agentserver.invocations; the new sample passes targeted Pyright.

Contribution Checklist

• The code builds clean without any errors or warnings for the changed sample files
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
  • Sample-only change. I ran focused sample syntax, Ruff, Pyright, and offline tool import checks instead of the full unit suite.
• Is this a breaking change? No.

[Copilot]

Pull request overview

Adds a new Python sample demonstrating how to expose API-key backed external research calls as Agent Framework async function tools, with an offline fallback so sample validation doesn’t require secrets.

Changes:

• Added a new xquik_function_tools.py sample implementing read-only Xquik function tools (search posts, user lookup, user posts, trends).
• Implemented a “no API key” path that returns deterministic local sample data.
• Added a tools/README.md indexing tool samples and documenting the Xquik sample setup.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/samples/02-agents/tools/xquik_function_tools.py	New sample implementing Xquik-backed async @tool functions with offline sample-data fallback and a runnable main().
python/samples/02-agents/tools/README.md	New README enumerating function tool samples and documenting the Xquik sample prerequisites.