Add shallow clone support

[Boomatang]

Closes #68

Overview

Introduces the ability to perform shallow clones with a depth of one, significantly improving clone speed when full commit history is not required. This is particularly useful when cloning to temporary directories for quick operations.

Implementation

The -S/--shallow flag has been added to enable shallow cloning. When set, the clone operation uses --depth=1, fetching only the latest commit without history.

How Acceptance Criteria is Met

The issue requested a clone depth flag to improve clone performance. The implementation addresses this by:

• Default behavior preserved: When the shallow flag is not set, repositories are cloned with full history
• Fast shallow clones: The -S/--shallow flag triggers a depth-1 clone, eliminating unnecessary history transfer
• Works with both clone modes: Shallow cloning is supported for both standard clones and worktree-based clones

Note: The current implementation uses a boolean flag for depth-1 clones rather than accepting arbitrary depth values. This simplifies the interface while addressing the primary use case of fast clones without history.

Usage

# Shallow clone to temporary directory
grab -t -S https://github.com/owner/repo

# Shallow clone with standard mode
grab -s -S https://github.com/owner/repo

Additional Changes

Fixed a memory leak in the Configuration cleanup logic by properly freeing allocated path strings in the deinit method.