Divide up tuning file modification from camera actions for recalibration.

* Ensure that funtions only called locally by recalibrate utils are private
* Move public API to the top of the recalibrate utils file
* Move files that only alter the tuning dictionary to their own file

This makes the recalibration API used by PiCamera much more clearly defined, which
helps to plan out how to allow for different models.

hardware-specific-tests/picamera2/test_tuning.py

@@ -8,20 +8,17 @@ from picamera2 import Picamera2
 from openflexure_microscope_server.things.camera import (
     picamera_recalibrate_utils as recalibrate_utils,
 )
+from openflexure_microscope_server.things.camera import (
+    picamera_tuning_file_utils as tf_utils,
+)
 
 
 MODEL = Picamera2.global_camera_info()[0]["Model"]
 
 
-def load_default_tuning():
-    """Return the default tuning file for the connected camera."""
-    fname = f"{MODEL}.json"
-    return Picamera2.load_tuning_file(fname)
-
-
 def generate_bad_tuning():
     """Return a tuning file with an invalid version number to force an error when loaded."""
-    default_tuning = load_default_tuning()
+    default_tuning = tf_utils.load_default_tuning()
     bad_tuning = default_tuning.copy()
     bad_tuning["version"] = 999
     return bad_tuning
@@ -58,7 +55,7 @@ def _test_bad_tuning_after_good_tuning(configure: bool = False):
     PiCamera2 behaviour does not expect the tuning file to be reloaded.
     """
     bad_tuning = generate_bad_tuning()
-    default_tuning = load_default_tuning()
+    default_tuning = tf_utils.load_default_tuning()
     print_tuning()
     print("opening camera with default tuning")
     with Picamera2(tuning=default_tuning) as cam: