Write a method findCountriesByCurrency that accepts a currency code (e.g., 'USD', 'EUR') and returns a List of country names that use that currency.

Make an HTTP GET request to the REST Countries API using the endpoint https://restcountries.com/v3.1/currency/{currencyCode} where {currencyCode} is replaced with the input parameter.

The API returns an array of country objects. Each country object contains a name field with a common property that holds the country name.

If the HTTP request fails, the API returns an error, or no countries are found, return an empty list.

Example 1: Find countries using USD

List<String> countries = findCountriesByCurrency('USD');
// Returns a list that includes 'United States', 'Ecuador', 'El Salvador', etc.
// (exact list may vary, but should include United States)

Example 2: Find countries using EUR

List<String> countries = findCountriesByCurrency('EUR');
// Returns a list of European countries that use the Euro
// (includes 'Germany', 'France', 'Spain', 'Italy', etc.)

Example 3: Invalid currency code

List<String> countries = findCountriesByCurrency('INVALID');
// Returns empty list [] because the currency code does not exist