Construct and store a PipelineEngine from loader.

        If get_loader is None, constructs an ExplodingPipelineEngine

def init_engine(self, get_loader):
        """
        Construct and store a PipelineEngine from loader.

        If get_loader is None, constructs an ExplodingPipelineEngine
        """
        if get_loader is not None:
            self.engine = SimplePipelineEngine(
                get_loader,
                self.asset_finder,
                self.default_pipeline_domain(self.trading_calendar),
            )
        else:
            self.engine = ExplodingPipelineEngine()