Add ability to filter commits by author

### Describe the feature or problem you’d like to solve

Should be able to filter list_commits by author

### Proposed solution

This exposes further aspects of the API that are important, it also reduces the number of fetches needed to get commits scoped to a particular author

### Example prompts or workflows (for tools/toolsets only)

- Analyze the most recent 100 commits by author 'user' 

