Python: MCP Error Handling Fix + Added Unit Tests

[giles17]

Motivation and Context

This PR improves error handling in the MCP connection logic by providing more specific and actionable error messages.
Resolves #1564

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.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_mcp.py	336	54	83%	132, 142–143, 164, 189, 204, 210, 214, 216, 298, 325, 356–357, 359–365, 367–369, 372–373, 417, 432, 450, 491, 504, 507–508, 512, 536, 539–540, 544, 575, 594, 596, 603–604, 623, 625, 631–634, 651–655, 780
TOTAL	11681	1901	83%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1371	98 💤	0 ❌	0 🔥	28.340s ⏱️

[Copilot]

Pull Request Overview

This PR improves error handling in the MCP (Model Context Protocol) connection logic by providing more specific and actionable error messages. The changes make it easier for developers to diagnose connection and initialization failures by including command details and distinguishing between different failure scenarios.

• Enhanced error messages in the connect() method to include command information and specific failure context
• Added comprehensive test coverage for error handling paths including connection failures, initialization failures, and cleanup verification
• Added tests for various edge cases in message handling, sampling callbacks, and client configuration

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 10 comments.

File	Description
python/packages/core/agent_framework/_mcp.py	Enhanced error messages in connect() method to provide command-specific context and wrapped initialization in try-catch for better error handling
python/packages/core/tests/core/test_mcp.py	Added extensive test coverage for error handling scenarios including connection failures, message handlers, sampling callbacks, and client parameter verification