After splitting From_To into From/To, standardise the city strings so only the first letter is uppercase (e.g. "londON" → "London"). Return the cleaned DataFrame.

Sample data: df:

            From_To  FlightNumber  RecentDelays              Airline
0      LoNDon_paris       10045.0      [23, 47]               KLM(!)
1      MAdrid_miLAN           NaN            []    <Air France> (12)
2  londON_StockhOlm       10065.0  [24, 43, 87]  (British Airways. )
3    Budapest_PaRis           NaN          [13]       12. Air France
4   Brussels_londOn       10085.0      [67, 32]          "Swiss Air"