fix: round base fee multiplier instead of ceiling it in fee estimation

[Kropiunig]

Summary

estimateFeesPerGas (and fillTransaction) apply the baseFeeMultiplier using fixed-point integer math:

const decimals = baseFeeMultiplier.toString().split('.')[1]?.length ?? 0
const denominator = 10 ** decimals
const multiply = (base: bigint) =>
  (base * BigInt(Math.ceil(baseFeeMultiplier * denominator))) / BigInt(denominator)

baseFeeMultiplier * denominator is mathematically an exact integer — that is the whole purpose of deriving decimals/denominator from the number's decimal places. It only needs a guard because of floating-point error, but Math.ceil guards it in the wrong direction. When the float product lands just above the integer, Math.ceil bumps it to the next integer:

• 1.09 * 100 === 109.00000000000001 → Math.ceil → 110 (applies 1.10, not 1.09)
• also affects 1.11 (→ 112), 1.12 (→ 113), and others

So a caller that sets baseFeeMultiplier: 1.09 silently gets a 1.10 multiplier. It is inconsistent, too: 1.15 (114.999…) already works because its float error falls below the integer, which shows the ceil is not an intentional round-up.

Fix

Use Math.round instead of Math.ceil. The target is always an exact integer and the float error is far below 0.5, so round recovers the intended value in every case (and matches ceil wherever ceil was already correct, e.g. 2.01). The same one-line fix applies to the duplicated multiplyFee helper in fillTransaction.

Test

Extended the existing args: chain \baseFeeMultiplier` override (value)test inestimateFeesPerGas.test.tswith a1.09case assertingmaxFeePerGas === baseFeePerGas * 109n / 100n + maxPriorityFeePerGas. It fails on main(produces* 110n / 100n`) and passes with the fix.

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Latest commit: 3682860

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commit: 3682860