Fix various static typing issues.

Author: KelSolaar

app.py

@@ -41,7 +41,7 @@
     __application_name__,
     external_scripts=os.environ.get("COLOUR_DASH_JS", "").split(","),
     external_stylesheets=os.environ.get("COLOUR_DASH_CSS", "").split(","),
-    server=SERVER,
+    server=SERVER,  # pyright: ignore
 )
 """
 *Dash* app.

apps/rgb_colourspace_transformation_matrix.py

@@ -245,7 +245,7 @@ def _uid(id_):
 def set_RGB_to_RGB_matrix_output(
     input_colourspace: str,
     output_colourspace: str,
-    chromatic_adaptation_transform: str,
+    chromatic_adaptation_transform: str | None,
     formatter: str,
     decimals: int,
 ) -> str:

index.py

@@ -3,6 +3,7 @@
 =====
 """
 
+import dash
 from dash.dependencies import Input, Output
 from dash.dcc import Link, Location, Markdown
 from dash.html import A, Div, H3, P
@@ -24,7 +25,7 @@
 
 
 @APP.callback(Output("apps", "children"), [Input("url", "pathname")])
-def load_app(app: APP):
+def load_app(app: dash.Dash):
     """
     Load given app into the appropriate :class:`Div` class instance.