In many real-world applications, converting temperatures between different units is a common task. For example, meteorologists, scientists, and engineers often need to convert temperatures from Celsius to Fahrenheit or Kelvin. In this challenge, you'll implement a function that converts temperatures between these units using logical operators and conditional statements.

Your task is to write a function convert_temperature that takes three parameters: a float representing the temperature value, a string representing the unit of the input temperature, and another string representing the desired unit for the output temperature. The function should return a Result type with either the converted temperature as a float or an error message if the input is invalid.

• The function should correctly convert temperatures between Celsius, Fahrenheit, and Kelvin.
• If the input unit or the desired output unit is not one of "C", "F", or "K", the function should return an error message: "Invalid unit".
• If the conversion is successful, the function should return the converted temperature as a float in the Ok variant of the Result.

The Celsius and Fahrenheit scales are named after the scientists Anders Celsius and Daniel Gabriel Fahrenheit, respectively. The Kelvin scale, on the other hand, is named after Lord Kelvin, a British physicist. Unlike the Celsius and Fahrenheit scales, which are based on the freezing and boiling points of water, the Kelvin scale is an absolute temperature scale based on the concept of absolute zero, the lowest possible temperature where all molecular motion ceases.

let result = convert_temperature(100.0, "C", "F");
assert_eq!(result, Ok(212.0));
 
let result = convert_temperature(32.0, "F", "C");
assert_eq!(result, Ok(0.0));
 
let result = convert_temperature(0.0, "C", "K");
assert_eq!(result, Ok(273.15));
 
let result = convert_temperature(300.0, "K", "C");
assert_eq!(result, Ok(26.85));
 
let result = convert_temperature(100.0, "C", "X");
assert_eq!(result, Err("Invalid unit".to_string()));

• To convert Celsius to Fahrenheit: F = C * (9/5) + 32
• To convert Fahrenheit to Celsius: C = (F - 32) * (5/9)
• To convert Celsius to Kelvin: K = C + 273.15
• To convert Kelvin to Celsius: C = K - 273.15
• Remember to handle invalid units with proper error messages.