fix(YAUDIT-COVE-6): correct yearn vault v2 preview functions

[penandlim]

Important

Coverage is currently disabled for this library due to forge limitations. TODO: Once the fix PR is merged, foundry-rs/foundry#7510 coverage should be re-enabled.

Describe your changes

Yearn Vault V2's deposit estimations cannot be made accurately with pricePerShare.
Therefore we need to copy the logic used Vault.vy for converting new asset to shares into the router contract for more accurate preview methods.

Relevant: https://github.com/yAudit/cove-report/issues/6

Checklist before requesting a review

• Title follows conventional commits style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• Newly added functions follow Check-effects-interaction
• Gas usage has been minimized (ex. Storage variable access is minimized)

[github-actions]

Changes to gas cost

Generated at commit: 5bbc05bb30955ca91c1fabc77589410b8d5b8bf6, compared to commit: 3a40ac31939e547b43e64f855d6e7f1b54ee9501

🧾 Summary (10% most significant diffs)

Contract	Method	Avg (+/-)	%
Yearn4626RouterExt	previewDeposits previewMints previewRedeems	+28,814 ❌ +36,058 ❌ +26,195 ❌	+111.05% +192.65% +100.49%

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Full diff report 👇

Contract	Deployment Cost (+/-)	Method	Min (+/-)	%	Avg (+/-)	%	Median (+/-)	%	Max (+/-)	%	# Calls (+/-)
Yearn4626RouterExt	3,453,286 (-20,322)	approve deposit multicall previewDeposits previewMints previewRedeems previewWithdraws pullToken redeemFromRouter redeemStakeDaoGauge redeemVaultV2 selfPermit withdrawFromRouter	25,150 (0) 101,172 (-31,729) 48,249 (-29) 673 (0) 627 (0) 672 (0) 628 (0) 30,866 (-109) 82,727 (0) 492,095 (+22) 132,876 (-517,822) 14,844 (-29) 140,463 (+22)	0.00% -23.87% -0.06% 0.00% 0.00% 0.00% 0.00% -0.35% 0.00% +0.00% -79.58% -0.19% +0.02%	52,294 (+16,158) 134,748 (+1,847) 425,084 (-34) 54,761 (+28,814) 54,775 (+36,058) 52,261 (+26,195) 37,167 (+13,402) 30,866 (-109) 146,255 (+19,276) 496,132 (+22) 359,052 (-353,742) 36,940 (-29) 142,812 (+22)	+44.71% +1.39% -0.01% +111.05% +192.65% +100.49% +56.39% -0.35% +15.18% +0.00% -49.63% -0.08% +0.02%	52,198 (+26,583) 121,743 (-11,158) 331,282 (-93) 55,372 (+28,514) 55,722 (+47,532) 52,921 (+26,561) 37,387 (+16,805) 30,866 (-109) 146,654 (-24) 496,132 (+22) 132,904 (-594,942) 36,940 (-29) 142,812 (+22)	+103.78% -8.40% -0.03% +106.17% +580.37% +100.76% +81.65% -0.35% -0.02% +0.00% -81.74% -0.08% +0.02%	52,663 (+513) 162,387 (+29,486) 895,723 (+22) 55,372 (+6,455) 55,722 (+6,458) 54,979 (+6,117) 66,387 (+17,469) 30,866 (-109) 151,532 (0) 500,169 (+22) 759,862 (+22) 59,037 (-29) 145,161 (+22)	+0.98% +22.19% +0.00% +13.20% +13.11% +12.52% +35.71% -0.35% 0.00% +0.00% +0.00% -0.05% +0.02%	1,029 (+1,024) 1,028 (+1,027) 3 (0) 261 (+255) 262 (+255) 262 (+255) 264 (+256) 1 (0) 516 (+513) 2 (0) 516 (+513) 2 (0) 2 (0)
YSDRewardsGauge	3,884,210 (0)	deposit redeem	2,732 (0) 8,327 (0)	0.00% 0.00%	193,008 (-27) 134,016 (-38)	-0.01% -0.03%	178,853 (0) 126,910 (0)	0.00% 0.00%	450,543 (0) 242,620 (0)	0.00% 0.00%	2,048 (0) 1,024 (0)
YearnGaugeStrategy	1,817,865 (0)	deposit report withdraw	30,717 (0) 58,515 (0) 74,620 (0)	0.00% 0.00% 0.00%	291,882 (+6) 302,960 (+2) 176,060 (+31)	+0.00% +0.00% +0.02%	308,482 (0) 69,644 (0) 201,040 (0)	0.00% 0.00% 0.00%	447,268 (0) 914,862 (+10) 256,348 (0)	0.00% +0.00% 0.00%	7,938 (0) 5,890 (0) 1,792 (0)
DYFIRedeemer	2,139,607 (0)	massRedeem	30,408 (0)	0.00%	441,232 (-65)	-0.01%	440,099 (0)	0.00%	689,094 (0)	0.00%	1,545 (0)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.56%. Comparing base (3a40ac3) to head (4f3fc77).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #302      +/-   ##
==========================================
- Coverage   97.57%   97.56%   -0.01%     
==========================================
  Files          19       19              
  Lines         988      987       -1     
  Branches      203      202       -1     
==========================================
- Hits          964      963       -1     
  Misses          1        1              
  Partials       23       23              

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[github-actions]

Slither report

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Summary