Don't import picamera to build system metadata

from openflexure_microscope.stage.mock import MockStage

from openflexure_microscope.camera.base import BaseCamera

from openflexure_microscope.camera.mock import MockStreamer

from openflexure_microscope.camera.pi import PiCameraStreamer

from openflexure_microscope.utilities import serialise_array_b64

from openflexure_microscope.plugins import PluginLoader

        }

        # Store an encoded copy of the PiCamera lens shading table, if it exists

        if self.camera and isinstance(self.camera, PiCameraStreamer):

        if self.camera and hasattr(self.camera, "read_lens_shading_table"):

            # Read LST. Returns None if no LST is active

            lst_arr = self.camera.read_lens_shading_table()

            system_metadata["lens_shading_table"] = {

                "b64_string": b64_string,

                "dtype": dtype,

                "shape": shape

                "shape": shape,

            }

        return system_metadata