chore(5-min-viz): clear out stale district/station info

if a station is selected and then de-selected, some information
associated with the station is not cleared, i.e., Absolute Post Mile
and Lanes stay greyed out, Streamlit's sign of "stale data". it turns
out that the st.empty() method sometimes needs some time to take effect
on the front-end. adding a small delay ensures that the DOM is ready
for st.empty().

Author: lalver1

pems_streamlit/src/pems_streamlit/apps/districts/app_stations.py

@@ -1,4 +1,5 @@
 import re
+import time
 
 import pandas as pd
 import streamlit as st
@@ -72,6 +73,7 @@ def main():
         map_placeholder = st.empty()
 
     with map_placeholder:
+        time.sleep(0.1)
         if station:
             df_selected_station = df_station_metadata.query("STATION_ID == @station")
             map_station_summary(df_selected_station)