add author field to list_commits for filtering

[davidbyttow]

Closes: #568

[Copilot]

Pull Request Overview

This pull request adds an optional "author" field to the list_commits API for filtering commits based on author information.

• Adds the "author" property to the input schema in tests.
• Updates the repositories function to retrieve and pass the new "author" parameter.
• Updates snapshots and documentation in README to reflect the new parameter.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/github/repositories_test.go	Adds tests to check for the new "author" property in schema and request.
pkg/github/repositories.go	Updates the input schema and passes "author" to the GitHub API.
pkg/github/toolsnaps/list_commits.snap	Updates the snapshot to include the "author" field.
README.md	Documents the new optional "author" parameter.