Does not rely on method cascading for immutability

[jama5262]

What does this PR do?

Remove method cascading reliability, simple chaining added

Example

Before

var jiffy = (
    Jiffy()
     ..add(hours: 3, days: 1)
     ..subtract(minutes: 30, months: 1)
    );
jiffy.yMMMMEEEEdjm; // Wednesday, February 3, 2021 6:07 PM

Now

var jiffy = Jiffy()
    .add(hours: 3, days: 1)
    .subtract(minutes: 30, months: 1);
    .yMMMMEEEEdjm; // Wednesday, February 3, 2021 6:07 PM