Implement update_work_item handler

[Tiberriver256]

This pull request introduces the implementation of the update_work_item handler for the Azure DevOps MCP server, along with comprehensive tests and necessary schema and interface updates. The key changes include the addition of the update_work_item handler, the creation of the corresponding schema and options, and the implementation of unit tests to ensure the functionality works as expected.

Implementation of update_work_item handler:

• Added updateWorkItem function to handle updating work items in src/operations/workitems.ts. This function constructs a JSON patch document based on provided options and updates the work item using Azure DevOps API.
• Introduced UpdateWorkItemSchema and UpdateWorkItemOptions to define the schema and options for updating a work item in src/operations/workitems.ts. [1] [2]

Server configuration:

• Registered the update_work_item handler in the Azure DevOps server configuration in src/server.ts. [1] [2]

Task management documentation:

• Moved Task 2.4 from the todo.md file to the doing.md file to reflect its current status. [1] [2]

Unit tests:

• Added comprehensive unit tests for the updateWorkItem function in tests/unit/operations/workitems-update-coverage.test.ts. These tests cover various scenarios, including minimal fields, all standard fields, additional fields, error handling, and API call verification.