Update part-03.md

[orun-sunny]

Type request as Observable for clarity and type safety

Description

By declaring the variable type, developers can better understand the asynchronous nature of the service methods and get improved IDE support (autocomplete, type inference, etc.).

Checklist

• I fully tested it as developer
• I tested the create and update flows to ensure everything works as expected

I verified that the modal closes, the form resets, and the list refreshes after submission

How to test it?

Open the form modal (e.g., "Add Book" or "Edit Book").

Fill in the form and submit.

Ensure the form triggers the proper API call (create or update).

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