docs: upgrade code snippets where freezed annotations are used.

[Xsantosh]

Description
This change updates the documentation code snippets to use the latest freezed annotations. The existing examples rely on older syntax. In particular, the abstract keyword will be added before class declarations to align with the updated freezed requirements.

Requirements

• Replace outdated freezed code snippets with the newer syntax.
• Add abstract before class declarations where required.
• Ensure all updated snippets compile correctly.
• Maintain consistency across the documentation.

[divyanshub024]

Hey @Xsantosh, Thanks for creating this issue. Would you like to work on this issue?

[Xsantosh]

Hi @divyanshub024,
Yes, Please assign this to me.

[divyanshub024]

@Xsantosh Assigned it to you 👍🏻