feat: add narrow weekday format for Persian calendar

[rezaaa]

Summary

Add narrow weekday format for Persian calendar to align with common Persian date formatting standards.

Motivation

While integrating react-day-picker with shadcn components, I noticed that the Persian calendar was displaying short weekday names (e.g., two characters), which is inconsistent with the standard Persian date formatting convention. In Persian interfaces, weekday names are typically displayed in their narrow format (single character) for better readability and space efficiency.

Since shadcn is broadly used across many projects, this change ensures that the Persian calendar follows the more common and expected format that users are familiar with in Persian applications.

Current format

Standard and common format from popular persian websites

Changes

• Added formatWeekdayName formatter to the Persian DayPicker component
• Changed from the default "cccccc" (short format) to "ccccc" (narrow format)
• This displays single-character weekday abbreviations (e.g., "ش" for Saturday) instead of two-character short names

Thanks

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Note

Low Risk
Localized formatting change scoped to weekday header rendering plus a small test addition; low risk outside of potential minor UI layout/translation differences.

Overview
Updates the Persian DayPicker wrapper to override formatters.formatWeekdayName, rendering narrow weekday labels (ccccc) when the active locale is Persian (fa*) and keeping the default short format (cccccc) for other locales.

Adds a regression test in examples/PersianEn.test.tsx to ensure the English Jalali example still shows two-letter weekday headers (e.g., "Th").

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[gpbl]

Thanks @rezaaa for the suggestion. I added a test in cfc4373 (#2895) and limited the shorter format to the fa locales.

[rezaaa]

@gpbl Thank You, I guess I didn't get any contribution :))

[gpbl]

@gpbl Thank You, I guess I didn't get any contribution :))

Yes :) your name appears here:
https://github.com/gpbl/react-day-picker/releases/tag/v9.13.1