[Backend] Introduce Notification Deduplication Service

[Abd-Standard]

Description

Prevent duplicate notifications from being processed when identical requests arrive within a configurable time window.

Tasks
Generate deduplication keys.
Cache recent requests.
Skip duplicate processing.
Record deduplication metrics.

Acceptance Criteria
Duplicate notifications are ignored.
Legitimate new requests continue processing.
Metrics accurately report skipped duplicates.

[eischideraa-unn]

I’d love to work on this issue. I’m experienced with solving similar problems, writing clean code, and understanding existing systems quickly.

For this issue, I’d approach it by identifying the root cause, implementing fixes that aligns with the current architecture, and testing properly to avoid regressions.

[grantfox-oss]

🦊 GrantFox — @eischideraa-unn has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #66)
2. Your PR will be reviewed by the Core-Foundry maintainers

Good luck! Track your progress on GrantFox.

[bashir1738]

Gm I would like to work on this issue ETA 3 hrs

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@eischideraa-unn's PR #71 was approved and merged by @Abd-Standard.

🏆 @eischideraa-unn: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (48 total points). Track your full progress on GrantFox.

👏 Great work, @eischideraa-unn! Keep contributing to Core-Foundry.