Traverse & Sequence

[SandroMaglione]

Added traverse and sequence methods to fpdart.

Specifically, this PR introduces the following methods:

• traverseList
• traverseListWithIndex
• sequenceList
• traverseListSeq [Task]
• traverseListWithIndexSeq [Task]
• sequenceListSeq [Task]

traverse and sequence allow to convert a List of a typeclass to a typeclass of List. These methods have been added to the following classes:

• Option
• Either
• IO
• IOEither
• Task
• TaskOption
• TaskEither

These methods have been implemented as static methods. Furthermore, an extension method to List has been also added.

For example, using traverse on Option is possible to validate a List:

/// "a40" is invalid 💥
final inputValues = ["10", "20", "30", "a40"];

/// Verify that all the values can be converted to [int] 🔐
///
/// If **any** of them is invalid, then the result is [None] 🙅‍♂️
final traverseOption = inputValues.traverseOption(
  (a) => Option.tryCatch(
    /// If `a` does not contain a valid integer literal a [FormatException] is thrown
    () => int.parse(a),
  ),
);

The function uses Option.tryCatch to map each element of the List to Option, resulting in List<Option>. traverse then converts List<Option> to Option<List>.