Feat/enable editing in middle

[AHED200]

This pull request introduces two new features to the Pinput widget: the ability to enable editing in the middle of a PIN and an option to call the onCompleted callback only when the input field loses focus. Additionally, it includes corresponding updates to the widget's properties, behavior, and test cases.

New Features:

• Enable Editing in the Middle of a PIN:

  • Added the enableEditingInMiddle property to allow users to tap on individual PIN positions to edit from that position. [1] [2] [3]
  • Updated _PinItem to handle taps and cursor positioning based on enableEditingInMiddle. [1] [2]

• Call onCompleted Only on Unfocus:

  • Introduced the callOnCompletedOnlyOnUnfocus property to control whether the onCompleted callback is triggered immediately upon PIN completion or only when the field loses focus. [1] [2] [3]