[Tests] Add Integration Tests for Multi-Channel Delivery

[Abd-Standard]

Description

Improve test coverage by validating notification delivery across multiple supported channels.

Tasks
Create end-to-end test scenarios.
Verify channel-specific payloads.
Simulate delivery failures.
Assert retry behavior.

Acceptance Criteria
Tests pass consistently.
Multi-channel scenarios are covered.
Failures produce meaningful logs.

[distributed-nerd]

can i work on this

[grantfox-oss]

🦊 GrantFox — @distributed-nerd 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 #65)
2. Your PR will be reviewed by the Core-Foundry maintainers

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[grantfox-oss]

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

@distributed-nerd's PR #69 was approved and merged by @Abd-Standard.

🏆 @distributed-nerd: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (118 total points). Track your full progress on GrantFox.

👏 Great work, @distributed-nerd! Keep contributing to Core-Foundry.