Can’t add files with `Project.addSourceFilesAtPaths()`

**Describe the bug**

Version: 19.0.0

**To Reproduce**

```ts
import { Project } from "ts-morph";

const project = new Project();

project.addSourceFilesAtPaths(["a/x.ts", "a/y.ts"]);
```

**Expected behavior**

Must behave like adding each file individually with `Project.addSourceFileAtPath()`.

Read CONTRIBUTING.md, then inspect Project.addSourceFilesAtPaths() alongside Project.addSourceFileAtPath(). Run the provided TypeScript reproduction and compare the resulting project files with those from adding each path individually; done means both approaches behave the same.

Written by the indexing model from the issue text.