Eliminate duplicates and improve performance

[suwakei]

Proposal:

1. Add .vscode to the allow list

Currently, IntelliJ IDEA’s .idea directories and .iml files are already excluded from conflict checks.
Similarly, Visual Studio Code (VS Code) is widely used, and .vscode directories are commonly present in project folders.

Adding .vscode to the allow list would improve the developer experience for VS Code users,
especially when using tools like create-next-app within existing project folders.

2. Use Set for performance and clarity

The current implementation uses an array (Array) and checks file inclusion with Array.prototype.includes().
Replacing this with a Set and using Set.prototype.has() offers two key advantages:

• Performance: Set.has() is generally faster than Array.includes() (O(1) vs O(n)). While the list is currently small, this is a good practice for scalability.
• Readability and semantic clarity: A Set clearly represents a unique collection of values, aligning with the goal of checking for duplicates.

These improvements help make the codebase more robust and user-friendly.

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: e430fd7

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer