Strengthen event schema validation and replay protections

[grantfox-oss]

Make event emission and replay handling resilient to malformed payloads, duplicate events, and schema drift during contract runtime.

• Affected files: app/contract/contracts/Folder/src/events.rs, app/contract/contracts/Folder/src/events_test.rs, app/contract/contracts/Folder/src/metadata.rs, app/contract/contracts/Folder/src/lib.rs, app/contract/contracts/Folder/src/nonce.rs, app/contract/contracts/Folder/src/test.rs, app/contract/contracts/Folder/src/types.rs, app/contract/README.md
• Acceptance criteria:
  • Event emission validates required fields, namespaces, and replay attributes before publishing.
  • Duplicate or replayed events are rejected or safely deduplicated according to the contract contract semantics.
  • Tests cover schema mismatch, invalid event topics, and deterministic replay-field enforcement.

[Nanafancy]

I will love to work on this issue kindly assign

[grantfox-oss]

🦊 GrantFox — @Nanafancy has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #560)
2. Your PR will be reviewed by the BlockDash-Studios maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

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

@Nanafancy's PR #567 was approved and merged by @MaryammAli.

🏆 @Nanafancy: You earned 40 FoxPoints for this contribution! Your current tier: Builder (1,208 total points). Track your full progress on GrantFox.

👏 Great work, @Nanafancy! Keep contributing to BlockDash-Studios.