refactor(notifications): Centralize notification state update logic

[cypherpepe]

The main improvement is the removal of repeated logic for filtering and updating notifications. This is achieved by centralizing it in the 'getUpdatedTopicState' function, making the reducer more readable and reducing potential errors from code duplication.

Description

This PR refactors the notifications reducer to improve code readability and reduce duplication. Previously, filtering and updating logic for notifications was duplicated in multiple cases (FETCH_NOTIFICATIONS_DONE, UNSHIFT_NEW_NOTIFICATIONS). This has now been centralized in a new helper function, getUpdatedTopicState, which handles filtering out existing notifications and updating the state consistently. As a result, the reducer is now cleaner, and the risk of introducing inconsistencies is minimized.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code refactor (optimization of existing code)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Fixes/Resolves (Optional)

This PR does not fix any issues specifically, but it improves the maintainability of the code by reducing redundancy and simplifying state updates for notifications.

Examples/Screenshots (Optional)

Before	After
Repeated logic in multiple cases	Centralized logic in one function

Checklist:

• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

Additional Information (Optional)

The getUpdatedTopicState function improves consistency across state updates by ensuring that notifications are filtered and updated in a unified way. This reduces the risk of errors or bugs that could arise from duplicate logic in the reducer.

[vercel]

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[Vineetkg20]

"Great refactor! Centralizing the notification state update logic in getUpdatedTopicState really improves the readability and maintainability of the reducer. By reducing duplication, it lowers the chance of inconsistencies, which is fantastic. One suggestion: perhaps adding a few more comments or inline documentation explaining the function’s purpose could help new contributors understand the logic quicker. Have you also tested this thoroughly to ensure there are no edge cases that were missed? Overall, excellent improvement!"

[cypherpepe]

@Vineetkg20 Done