Add multi-asset funding imbalance tests

[edehvictor]

Summary

Add contract tests for payroll batches funded with multiple assets where one asset is overfunded and another is underfunded.

Why This Matters

Multi-asset payroll can appear funded overall while still missing the exact asset needed for some employees.

Suggested Files

• contracts/src/treasury.rs
• contracts/src/payroll.rs
• contracts/tests/multi_asset_imbalance.rs

Tasks

• Build fixtures with two or more payroll assets.
• Assert execution fails when any required asset is underfunded.
• Assert surplus in another asset does not hide a deficit.
• Document asset-specific readiness checks.

Acceptance Criteria

• Each asset balance is validated independently.
• Overfunding one asset cannot offset underfunding another.
• Failure messages identify the deficient asset.
• Tests cover balanced, underfunded, and surplus cases.

Coordination

Join the Telegram channel for proper coordination: https://t.me/zkpayroll