mark all $.style subfields as optional

because $.style is itself optional and all the subfields are set to
default values.

src/plot.py

@@ -18,22 +18,22 @@ class Point(TypedDict):
     e: Optional[float]
 
 class MarkerStyle(TypedDict):
-    shape: str
-    size: int
+    shape: Optional[str]
+    size: Optional[int]
 
 class LineStyle(TypedDict):
-    marker: MarkerStyle
-    type: str
-    width: int
-    alpha: float
+    marker: Optional[MarkerStyle]
+    type: Optional[str]
+    width: Optional[int]
+    alpha: Optional[float]
 
 class ErrorStyle(TypedDict):
-    alpha: float
+    alpha: Optional[float]
 
 class Style(TypedDict):
-    color: str
-    line: LineStyle
-    error: ErrorStyle
+    color: Optional[str]
+    line: Optional[LineStyle]
+    error: Optional[ErrorStyle]
 
 class Graph(TypedDict):
     name: Optional[str]