feat: add path to XcodeProj and XCWorkspace

[ajkolean]

Resolves tuist/XcodeGraph#87 (comment)

Short description 📝

This PR introduces an optional projectPath property to XcodeProj, allowing the project to be initialized and managed without requiring a file system path. It maintains full backward compatibility for existing users while offering more flexibility for in-memory project constructions or integrations with path management logic outside of XcodeProj.

Solution 📦

The projectPath property is now optional. When loading from a file system path, projectPath is set automatically. If users create XcodeProj instances in memory using the new initializer, projectPath can remain nil. This approach preserves existing behavior while enabling new use cases, such as working with XcodeProj in environments where a project might not yet exist on disk.

Implementation 👩‍💻👨‍💻

• Introduce projectPath: Path? as an optional property in XcodeProj.
• Update init(path:) to set projectPath when loading from disk.
• Add a new initializer that allows creating XcodeProj instances without a projectPath.
• Include projectPath in the equality check to distinguish between projects referencing different directories.
• Retain backward compatibility and do not alter existing file loading or writing behavior.

[fortmarek]

Just some minor comments 🙂

[fortmarek]

I'd also add path to the XCWorkspace: https://github.com/tuist/XcodeProj/blob/main/Sources/XcodeProj/Workspace/XCWorkspace.swift

I'll leave it up to you if you wanna do it in this PR or in a subsequent one.

[fortmarek]

We also really need to migrate the paths from PathKit to our Path. The needed conversion between the paths is unnecessary pain in the XcodeGraphMapper