fix: add duplicate detection and escrow ID mapping to deposit_partial

[tolulopedd26]

Summary

Closes #13

Deployment Checklist

• I reviewed documentation/deployment-checklist.md.
• Required checks are green: format, clippy, full tests, benchmarks, and upgrade harness.
• Event schema is locked with the canonical schema test.
• Governance requirements are documented: threshold keys and pause policy.
• The environment registry has been updated for each affected network.
• Testnet validation was completed before any mainnet promotion.
• Post-deploy validation includes metadata view, health check, and event emission smoke test.
• Mainnet steps are explicit and repeatable, or this PR is not a mainnet release.

Notes

[MaryammAli]

LGTM