Fix date parsing to respect user's configured date format in datagrid

[Copilot]

Date input parsing in datagrid fields ignored the user's configured date format (e.g., D/M/Y) and always used locale-based parsing (M/D/Y for en-US). Typing "2/9/2025" with D/M/Y format selected September 2nd in the UI but parsed as February 9th.

Changes

Modified parseDateTimeStr() in date_time_text_field.dart

• Parse using configured date format pattern first (strict then lenient)
• Handle date+time combined formats when includeTime is enabled
• Fall back to AnyDate for natural language input ("tomorrow", etc.)

Added test coverage

• Test case verifying DayMonthYear, US, and Local format parsing
• Validates "2/9/2025" → Sept 2 for D/M/Y, Feb 9 for M/D/Y

Example

// Before: always used locale-based parsing
final parser = AnyDate.fromLocale(locale);
final result = parser.tryParse(string);

// After: respects configured format
try {
  return dateFormat.parseStrict(trimmedString); // e.g., dd/MM/y
} catch (_) {
  // Fall back to lenient parsing, date+time formats, then AnyDate
}

Maintains backward compatibility with natural language dates and all existing date format patterns (Local, US, ISO, Friendly, DayMonthYear).

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Bug] Date format not respected in date type for datagrid</issue_title>
<issue_description>### Bug Description

My AppFlowy app is set to D/M/Y format. When I type in the date 2/9/2025 in a datagrid date field, it selects February 9th, 2025, not September 2nd, 2025. The format in the input seems to be forced M/D/Y. It only works correctly if the D portion is above 12.

How to Reproduce

Try putting a date into a date field that uses a day and month below 12.

Expected Behavior

Respect the Date format I've selected for the app.

Operating System

MacOS

AppFlowy Version(s)

10.0.2

Screenshots

No response

Additional Context

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

@LucasXu0 It can be reproduced in the latest version.

</comment_new>

• Fixes [Bug] Date format not respected in date type for datagrid #8310

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