Python: Add documentation for declaration-only tools and middleware ordering

[giles17]

Motivation and Context

Adds documentation for declaration-only tools and middleware execution ordering.

Changes

• _tools.py: Document func parameter in @tool decorator and FunctionTool class explaining declaration-only tool usage (func=None)
• agent_and_run_level_middleware.py: Add detailed middleware execution ordering documentation

Linked Issues

Closes #3580
Closes #3582

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

Adds clarifying documentation in the Python Agent Framework for (1) declaration-only tools and (2) middleware execution ordering when mixing agent-level and run-level middleware.

Changes:

• Document func=None behavior for declaration-only tools in FunctionTool and @tool decorator docs, including an example.
• Add a detailed middleware execution ordering explanation to the agent/run-level middleware sample.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
python/samples/getting_started/middleware/agent_and_run_level_middleware.py	Expands sample documentation to explain agent-level vs run-level middleware ordering with an execution diagram.
python/packages/core/agent_framework/_tools.py	Documents func=None for declaration-only tools in FunctionTool and tool() docstrings and adds an example.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_tools.py	789	85	89%	232, 278, 329, 331, 359, 529, 564–565, 676, 678, 698, 716, 730, 742, 747, 749, 756, 789, 860–862, 903, 925–953, 988, 996, 1237, 1489, 1546, 1550, 1629–1633, 1651, 1653–1654, 1759, 1763, 1813, 1815, 1831, 1833, 1897, 1924, 1977, 2045, 2224–2225, 2252, 2260, 2273, 2283–2284, 2319, 2375, 2407
TOTAL	16592	2059	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3925	225 💤	0 ❌	0 🔥	1m 8s ⏱️