Fixed DatePickerTheme import collision on Flutter 3.13.4

[xxMrPHDxx]

The following error pops up while I'm trying to build. I'm fixing it by using aliases.

../../.pub-cache/hosted/pub.dev/flutter_datetime_picker-1.5.1/lib/flutter_datetime_picker.dart:199:31: Error: 'DatePickerTheme' is imported from both 'package:flutter/src/material/date_picker_theme.dart' and 'package:flutter_datetime_picker/src/datetime_picker_theme.dart'.
        this.theme = theme ?? DatePickerTheme(),
                              ^^^^^^^^^^^^^^^
Target kernel_snapshot failed: Exception


FAILURE: Build failed with an exception.