Vehicle Trip History

Originated from embeddedt/OpenTTD-modded (Batch 1 port), adapted to jrpm's new string and date APIs.

Feature

Every vehicle remembers data from its last 10 trips, viewable via the new History button in the vehicle details window:

Column	Meaning
Received	Date when cargo was received for this trip
Profit	Profit for this trip (negative values shown in yellow)
% Change	Profit change percentage compared to the previous trip (green + / red -)
TBT	Time between trips (days)
Change	Time change compared to the previous trip (days)
Occupancy	Average load/passenger rate for this trip (%)

The bottom of the window also shows summary statistics:

Total income for the last N trips: Total profit for N trips + average daily profit per trip
Average trip length: Average trip interval (days)
Improvement over last N trips: Overall profit change percentage

AddValue: When a vehicle completes a transport run (CargoPayment destructor), records profit, date, occupancy, and station-to-station distance
NewRound: When a vehicle reaches the first destination according to its timetable, starts a new trip
Occupancy: Captured when the vehicle leaves a station (reuses jrpm's existing trip_occupancy mechanism)

Data is NOSAVE (runtime only, not written to saves), so no save version bump is needed, and old saves are fully compatible
New window class WindowClass::VehicleTripHistory, window ID is the vehicle ID
The vehicle details window (train/non-train) title bar gets a new History button
History windows are automatically closed when the vehicle is deleted

src/triphistory.h / src/triphistory_cmd.cpp / src/triphistory_gui.cpp (new)
src/vehicle_base.h (Vehicle adds trip_history field)
src/economy.cpp (CargoPayment destructor records trip)
src/timetable_cmd.cpp (reaching first station starts a new trip)
src/vehicle_gui.cpp / src/widgets/vehicle_widget.h (History button)
src/lang/english.txt (STR_TRIP_HISTORY_* strings)