feat: 👔 allow same day selection in range selection

[moazelsawaf]

Hello 👋🏻

I'd like to start by expressing my gratitude for your package – it has significantly benefited my Flutter projects. 💪🏻💙

While integrating it into one of my applications, I noticed a minor limitation: the inability for users to select the same day within a range, which my app requires.

To address this, I've made some adjustments to the code. Following thorough testing, I'm pleased to confirm that the functionality now operates smoothly without any adverse effects on other features.

Interestingly, it appears I'm not alone in seeking this enhancement. There's an existing issue (#707) that also highlights the need for this feature, and I believe this pull request will effectively resolve it.

I trust this update will prove valuable to both my project and potentially others facing similar requirements. 🙏🏻

Thank you sincerely for your ongoing contributions to the Flutter community. 💙 🙏🏻