buyCollateral tests refactoring

[VladyslavPerederWoof]

Summary

Rewrites the buyCollateral test suite to target CometWithExtendedAssetList (24 collateral assets) and align with the project's test writing conventions.

Key changes

• Migrated from makeProtocol() to makeConfigurator() — the main describe now deploys a full configurator/proxy stack with 24 collateral assets (ASSET0..ASSET23), exercising CometWithExtendedAssetList + CometExtAssetList through the proxy.
• Eliminated forbidden patterns — removed wait(), portfolio(), event(), and harness state-manipulation helpers (setTotalsBasic, setTotalsCollateral, setCollateralBalance). All state is now established through real protocol interactions (supply, withdraw, absorb, buyCollateral).
• Adopted flow-based describe structure with atomic it blocks — each it checks exactly one value (a single balance, a single event, a single revert). Actions like time advances and contract calls are their own it blocks, making failures immediately identifiable.
• Added takeSnapshot / snapshot.restore() isolation — independent describe blocks share a common starting state via snapshots instead of re-deploying the protocol.
• Switched to revertedWithCustomError — replaces string-based revertedWith("custom error '...()'") assertions with typed custom error assertions (e.g., .to.be.revertedWithCustomError(comet, 'NotForSale')).

New test coverage

• Revert cases (grouped under describe('revert cases')):
  • Paused — buying when isBuyPaused is true
  • NotForSale — reserves equal targetReserves exactly, and reserves exceed targetReserves
  • TooMuchSlippage — minAmount exceeds quoted collateral
  • InsufficientReserves — single buy exceeds collateral reserves, and a second consecutive buy exceeds remaining reserves after a first successful buy
• Successful purchase — buyer is the recipient — verifies events (BuyCollateral, base Transfer, collateral Transfer), alice/comet token balances, protocol reserves, and collateral reserves
• Successful purchase — recipient differs from buyer — alice pays, bob receives collateral; verifies alice collateral balance unchanged, bob balance increased
• Collateral for sale when reserves are negative — uses configurator to set targetReserves=0, creates bad debt via absorb (price drop + liquidation), then buys collateral with negative reserves
• Collateral reserves vs user-owned collateral — verifies only excess (non-user-owned) collateral is buyable; alice's on-protocol position is unchanged after a buy from reserves
• All 24 collateral assets — extended asset list coverage — sequential buy across all 24 packed AssetList slots, validating getAssetInfoByAddress inside quoteCollateral/buyCollateral for every slot
• Fee-on-transfer tokens — split into two sub-describes: base token with 1% fee (event records net, not gross) and collateral token with 1% fee (event records gross, buyer receives net)
• Reentrancy — retained and cleaned up: reentrant buyCollateral via EvilToken base is blocked (ReentrantCallBlocked), and a state-comparison proof shows reentrant supplyFrom during buyCollateral is silently blocked (evil totalSupplyBase = 0 vs normal totalSupplyBase = 1e6)