Python: fix: @ai_function doesn't properly handle 'self' param

[eavanvalkenburg]

Motivation and Context

Adds the ability to use the @ai_function decorator within a class definition.
Adds tests to validate, including tests of cross instance execution of the tools.

Fixes #1343

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull Request Overview

This PR adds support for using the @ai_function decorator on class methods, fixing issue #1343. The implementation uses Python's descriptor protocol to properly bind class instances to decorated methods.

Key Changes:

• Implements the __get__ descriptor method to handle method binding when accessing decorated methods from class instances
• Adds _instance attribute to track bound instances and properly inject self during function calls
• Ensures that self and cls parameters are excluded from the generated parameter schemas

Reviewed Changes

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

File	Description
python/packages/core/agent_framework/_tools.py	Implements descriptor protocol (__get__) for method binding and updates __call__ to inject bound instance
python/packages/core/tests/core/test_tools.py	Adds comprehensive tests for decorator usage in classes and verifies shared state behavior across multiple tool instances

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_tools.py	617	69	88%	225, 271, 322, 324, 487, 519–520, 621, 623, 636, 654, 668, 680, 685, 687, 694, 727, 776–778, 816, 839, 841–850, 859–865, 893, 903, 941, 950, 952, 955, 961, 1328–1332, 1432, 1501, 1602, 1608, 1649–1650, 1782, 1821–1822, 1850–1852, 1887–1888, 1951–1952, 1959–1960
TOTAL	14985	2228	85%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2041	129 💤	0 ❌	0 🔥	39.985s ⏱️