Add duration in new leave notification

[cp-pratik-k]

Purpose

Show leave duration in new leave request notfication

Summary of Changes

• Add duration in notification

Test steps

• Run flutter test

Conformity

• Followed git guidelines for creating commit messages and Pull Request guidelines.
• Self-approved the PR - reviewed the PR as a reviewer and gave it self-approval if everything is ok. If not, made the required changes.
• Ensured that the PR satisfies all specified requirements in the ticket, including bug fixes and new features.
• Provided test steps, including steps to reproduce the issue or test the new functionality, ensuring other team members can verify the changes.
• Added/Updated proper code comments to make it easy-to-understand for other developers.
• Reused code (if the same code was written twice, made it common and reused it at both places).
• Removed unused or commented code if not required.
• Ensured proper Dart naming conventions were used for variables, classes, and methods.
• Localized user-facing strings.
• Included screenshots/videos of behavior changes: Provided visual evidence of any changes to UI or behavior for easier review and understanding in the PR description.
• Implemented proper error handling: Ensured that the code anticipated and handled potential errors and edge cases gracefully.
• Avoided introducing technical debt: If the PR introduces technical debt, created and linked appropriate tickets for future resolution.
• Included relevant unit tests: Wrote unit tests that focused on testing behavior and functionality, rather than merely covering lines of code.
• Ensured code was performant and scalable: Verified that the changes did not introduce performance issues or bottlenecks and could scale as needed.
• Ensured comments were up-to-date and relevant to the code to describe complex logic and to add understanding for other developers.
• Marked the PR as ready before submitting it for review.