feat: add locale prop to CupertinoDatePicker, DatePicker, DateRangePicker, TimePicker

[ndonkoHenri]

Fix #6009

Test Code

import flet as ft


def main(page: ft.Page):
    page.horizontal_alignment = ft.CrossAxisAlignment.CENTER

    page.add(
        ft.Button(
            content="Pick time (zh_Hans locale)",
            icon=ft.Icons.CALENDAR_MONTH,
            on_click=lambda e: page.show_dialog(
                ft.TimePicker(locale=ft.Locale("zh", "Hans"))
            ),
        )
    )


ft.run(main)

Summary by Sourcery

Add per-control locale overrides to date and time pickers and tighten locale configuration/validation across Flutter and Python layers.

New Features:

• Introduce an optional locale property for CupertinoDatePicker, DatePicker, DateRangePicker, and TimePicker controls to allow overriding page/system locale per picker instance.

Enhancements:

• Refine Python Locale and LocaleConfiguration types with stronger defaults, validation, and detailed documentation for language/region/script handling and resolution behaviour.
• Filter supported locales on the Flutter side to only include those supported by Flutter localization delegates and add a Locale.isSupportedByDelegates helper.
• Refactor multiple Dart enum parsing helpers to share a common generic parseEnum utility.
• Export the new Dart enums utility module for broader reuse.

Documentation:

• Add example apps demonstrating custom locales for CupertinoDatePicker, DatePicker, DateRangePicker, and TimePicker.

Tests:

• Extend and restructure integration tests for CupertinoDatePicker, DatePicker, DateRangePicker, and TimePicker to cover locale overrides via screenshots and per-test app fixtures.

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Pull request overview

This pull request adds a locale property to CupertinoDatePicker, DatePicker, DateRangePicker, and TimePicker controls to address issue #6009, which reported that date pickers were not respecting the page locale setting.

Changes:

• Enhanced the Locale and LocaleConfiguration classes with improved validation and detailed documentation
• Added a locale property to all four picker controls (DatePicker, DateRangePicker, TimePicker, CupertinoDatePicker)
• Implemented Dart-side locale override functionality using Localizations.override
• Added comprehensive test coverage and example files demonstrating the new feature

Reviewed changes

Copilot reviewed 21 out of 27 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk/python/packages/flet/src/flet/controls/types.py	Enhanced Locale and LocaleConfiguration dataclasses with validation, default values, and comprehensive documentation
sdk/python/packages/flet/src/flet/controls/material/time_picker.py	Added locale property to TimePicker
sdk/python/packages/flet/src/flet/controls/material/date_range_picker.py	Added locale property to DateRangePicker
sdk/python/packages/flet/src/flet/controls/material/date_picker.py	Added locale property to DatePicker
sdk/python/packages/flet/src/flet/controls/cupertino/cupertino_date_picker.py	Added locale property to CupertinoDatePicker
packages/flet/lib/src/controls/*.dart	Implemented locale override using Localizations.override wrapper
packages/flet/lib/src/utils/locale.dart	Added locale validation against Flutter's supported locales
packages/flet/lib/src/utils/enums.dart	Created reusable enum parsing utility
packages/flet/lib/src/utils/misc.dart	Refactored to use new parseEnum utility
Test files	Added locale-specific tests with golden image comparisons
Example files	Added custom_locale.py examples for each picker control

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