Fix for headlineSmall Font Size in OmniDateTimePicker

[binzheng]

Description:

Font Issue on iPad 10th Generation:
When setting the headlineSmall property to fontSize: 34, the text appears to be cut off, especially on an iPad 10th generation. Specifically, 2-digit numbers are only displaying as a single digit, which affects the usability.

Steps to Reproduce:
Set up the OmniDateTimePicker with headlineSmall set to fontSize: 34.
Open the picker on an iPad 10th generation device or simulator.
Notice that the numbers get cut off.
Expected Behavior:
All numbers, including 2-digit numbers, should display completely without getting cut off.

Actual Behavior:
2-digit numbers are getting cut off and only showing as a single digit.

Environment:
Flutter version: [your_flutter_version]
OmniDateTimePicker version: 1.0.8