I need to extend the SWC parsing APIs to support both `Buffer` and `string` inputs for the source code. Please update the `parse` and `parse_sync` functions to accept `Either<Buffer, String>` instead of just `String`. Add a helper function to convert the `Either` type into a UTF-8 string, using `String::from_utf8_lossy` for buffers to handle invalid characters gracefully. Ensure the TypeScript definitions in `binding.d.ts` reflect the new parameter types. Include unit tests for both buffer and string inputs in `api_test.js`, verifying that asynchronous and synchronous parsing produce identical results regardless of input type. Maintain backward compatibility with existing string-based calls and ensure the `filename` fallback logic remains unchanged. Simplify the `src` handling to avoid code duplication between async/sync paths.