This commit adds a new static method `isInstanceOf` to the `BError` class in `src/error.ts`. The method checks if a given object is an instance of `BError` or if it is an instance of the base `Error` class with the same name.

Replaced the usage of the `errorCustomClass` function with the `causedError` function in the `BError` class in `src/error.ts` file. This change improves the error handling functionality.