Add tool for project fields and items

[JoannaaKL]

This pr adds:

• get_project_field tool for user and org
• get_project_item tool for user and org
• list_project_items tool for user and org

Updates:

• projectNumber tool param to project_number

After this PR is merged last chunk of project tools to be added are:

• add_project_item
• delete_project_item
• update_project_item

It's worth noting that we are returning minimal project v2 and not the full response.
Implements #44

[Copilot]

Pull Request Overview

Adds a new get_project_field tool for retrieving specific project fields from GitHub projects for both users and organizations. This PR implements issue #44 by creating functionality to fetch individual project field details by field ID.

• Implements GetProjectField function with support for user and org projects
• Adds comprehensive test coverage for the new tool including error cases
• Updates existing list_project_fields tool to use correct numeric type for project numbers

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/github/projects.go	Adds GetProjectField function and fixes projectNumber type in ListProjectFields
pkg/github/projects_test.go	Adds comprehensive test cases for GetProjectField tool
pkg/github/toolsnaps/get_project_field.snap	Tool snapshot for new get_project_field tool
pkg/github/toolsnaps/list_project_fields.snap	Updated snapshot reflecting projectNumber type change
README.md	Updated documentation to reflect projectNumber type change

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[kerobbi]

Just a non blocking nit, everything else looks solid!