docs(kepler-problem): fix typing of kepler problem tutorial

#82

docs/tutorials/kepler_problem.py

@@ -25,6 +25,7 @@
 import numpy as np
 import pandas as pd
 import plotly.express as px
+import plotly.graph_objects as go
 
 from hamilflow.models.kepler_problem import Kepler2D
 
@@ -51,21 +52,25 @@
 )
 
 # %% [markdown]
-# We define the time steps for a Kepler system. In this example, we create 101 time steps.
+# We define the time steps for a Kepler system. In this example, we create 401 time steps, also with some some negative timestamps for a more symmetric trajectory.
 
 # %%
 t = np.linspace(-20, 20, 401)
 
 # %% [markdown]
-# Orbit time series data is generated by calling the object `k2d`
+# Orbit time series data is generated by calling the object `k2d`, as the data generation is done in the `__call__` method.
 
 # %%
 df_p_1 = k2d(t=t)
 df_p_1  # noqa: B018
 
 
 # %%
-def visualize_orbit(dataframe: pd.DataFrame):  # noqa: D103, ANN201
+def visualize_orbit(dataframe: pd.DataFrame) -> go.Figure:
+    """Plot out the trajectory in a polar coordinate.
+
+    :param dataframe: dataframe containing the trajectory data
+    """
     fig = px.line_polar(
         dataframe.assign(
             phi_degree=dataframe.phi / (2 * np.pi) * 360,