[Improvement] Run test in parallel

### What would you like to be improved?

We can run all tests simultaneously to reduce testing time.

### How should we improve?

We can use the following code to run the test simultaneously.

```kotlin
tasks.configureEach {
maxParallelForks = 8
}
```

Start from the repository's test build configuration and review how the Gradle Kotlin DSL configures Test tasks. Apply the proposed parallel-fork setting, then run the test suite to confirm tests complete successfully and verify that test execution time is reduced without introducing failures.

Written by the indexing model from the issue text.