fix(staker): replace wrapping Mul with MulDiv in reward scaling

[notJoon]

Description

• Replace Mul(rewardAcc, liquidity) with MulDiv(rewardAcc, liquidity * rewardPerSecond, q128) to use a 512 bit intermediate instead of a 256-bit wrapping multiplication

Summary by CodeRabbit

• Bug Fixes

  • Improved precision in reward scaling calculations by optimizing the arithmetic computation path to prevent intermediate overflow issues.

• Tests

  • Added test coverage for reward scaler precision validation to ensure calculation accuracy across various scenarios.

[coderabbitai]

Walkthrough

Refactored reward scaling computation in RewardState.rewardPerWarmup to consolidate two arithmetic steps into a single MulDiv operation via new helper method scaleReward. This prevents intermediate wrapping from separate multiplications. Added test TestRewardScalerPrecision to validate the new approach and detect divergence from the previous computation path.

Changes

Cohort / File(s)	Summary
Reward Scaling Refactoring contract/r/gnoswap/staker/v1/reward_calculation_pool.gno	Extracted reward scaling logic into new helper method scaleReward that combines deposit.Liquidity() * rewardPerSecond and performs a single MulDiv operation, replacing the prior two-step multiplication approach to avoid intermediate wrapping.
Test Suite Updates contract/r/gnoswap/staker/v1/reward_calculation_pool_test.gno	Updated imports and added TestRewardScalerPrecision test that validates the new combined scaler approach, verifies expected u256 outputs, and asserts divergence from the old two-step approach when wrapping occurs.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: replacing a wrapping multiplication with MulDiv in reward scaling logic within the staker module.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/staker-reward-mul-overflow

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

contract/r/gnoswap/staker/v1/reward_calculation_pool_test.gno (1)

952-962: Exercise the production helper here.

Lines 952-962 re-derive the formula instead of calling RewardState.scaleReward or rewardPerWarmup, so this test can stay green even if the implementation under review regresses or starts reading the wrong liquidity source.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f80fe1ed-4ddc-481e-a051-788c596f025d

📥 Commits

Reviewing files that changed from the base of the PR and between bef2541 and a5523f9.

📒 Files selected for processing (2)

• contract/r/gnoswap/staker/v1/reward_calculation_pool.gno
• contract/r/gnoswap/staker/v1/reward_calculation_pool_test.gno