utility: Add function for calculating a rounded division

Make weather service use it.

src/components/ble/SimpleWeatherService.h

@@ -32,6 +32,7 @@
 #undef min
 
 #include "components/datetime/DateTimeController.h"
+#include "utility/Math.h"
 
 int WeatherCallback(uint16_t connHandle, uint16_t attrHandle, struct ble_gatt_access_ctxt* ctxt, void* arg);
 
@@ -75,13 +76,11 @@ namespace Pinetime {
         }
 
         [[nodiscard]] int16_t Celsius() const {
-          int16_t temp = PreciseCelsius();
-          return (temp + (temp >= 0 ? 50 : -50)) / 100;
+          return Utility::RoundedDiv(PreciseCelsius(), 100u);
         }
 
         [[nodiscard]] int16_t Fahrenheit() const {
-          int16_t temp = PreciseFahrenheit();
-          return (temp + (temp >= 0 ? 50 : -50)) / 100;
+          return Utility::RoundedDiv(PreciseFahrenheit(), 100u);
         }
 
         bool operator==(const Temperature& other) const {

src/utility/Math.h

@@ -1,10 +1,15 @@
 #pragma once
 
 #include <cstdint>
+#include <concepts>
 
 namespace Pinetime {
   namespace Utility {
     // returns the arcsin of `arg`. asin(-32767) = -90, asin(32767) = 90
     int16_t Asin(int16_t arg);
+
+    static constexpr auto RoundedDiv(std::integral auto dividend, std::unsigned_integral auto divisor) -> decltype(dividend / divisor) {
+      return (dividend + (dividend >= 0 ? divisor : -divisor) / 2) / divisor;
+    }
   }
 }