Python: Added explicit schema handling to @tool decorator

[dmytrostruk]

Motivation and Context

Resolves: #3579

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.

[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, 667, 669, 689, 707, 721, 733, 738, 740, 747, 780, 851–853, 894, 916–944, 979, 987, 1228, 1462, 1519, 1523, 1602–1606, 1624, 1626–1627, 1732, 1736, 1786, 1788, 1804, 1806, 1870, 1897, 1950, 2018, 2197–2198, 2225, 2233, 2246, 2256–2257, 2292, 2348, 2380
TOTAL	16592	2059	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3925	225 💤	0 ❌	0 🔥	1m 11s ⏱️

[Copilot]

Pull request overview

Adds first-class support for supplying an explicit input schema to the Python @tool decorator, enabling callers to bypass signature-based schema inference (per issue #3579).

Changes:

• Added a schema parameter to agent_framework.tool() that is forwarded to FunctionTool(input_model=...).
• Added unit tests covering explicit schema usage via both Pydantic models and JSON-schema-like dicts.
• Added a new getting-started sample and updated the tools README to document explicit schema usage.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
python/packages/core/agent_framework/_tools.py	Extends @tool to accept an explicit schema and updates docstring/docs.
python/packages/core/tests/core/test_tools.py	Adds coverage for @tool(schema=...) with Pydantic, dict schema, and schema=None.
python/samples/getting_started/tools/function_tool_with_explicit_schema.py	New sample demonstrating explicit schema usage.
python/samples/getting_started/tools/README.md	Documents the new explicit-schema capability and links the new sample.

Comments suppressed due to low confidence (1)

python/samples/getting_started/tools/function_tool_with_explicit_schema.py:60

• The schema above declares a default for timezone (making it effectively optional), but get_current_time() requires timezone with no default in the function signature. Consider either adding a default in the signature (e.g., timezone="UTC") or marking it as required in the schema to keep behavior consistent.

def get_current_time(timezone: str) -> str:
    """Get the current time."""