Load the encoder `name` from the model directory.

def load_encoder(self, name:str, device:torch.device=None):
        "Load the encoder `name` from the model directory."
        encoder = get_model(self.model)[0]
        if device is None: device = self.data.device
        if hasattr(encoder, 'module'): encoder = encoder.module
        encoder.load_state_dict(torch.load(self.path/self.model_dir/f'{name}.pth'))
        encoder.load_state_dict(torch.load(self.path/self.model_dir/f'{name}.pth', map_location=device))
        self.freeze()