Temperature Converter

A temperature widget needs two conversion helpers and one formatting helper. Keep the math separate from the display text so each function has one clear job.

1. `celsiusToFahrenheit(celsius)` should convert Celsius to Fahrenheit and return the number.
2. `fahrenheitToCelsius(fahrenheit)` should convert Fahrenheit to Celsius and return the number.
3. `formatTemperature(value, unit)` should return display text such as `"77 F"` or `"20 C"`.