⚡️ Optimize Pow2 Padding

[0xClandestine]

Description

⚡️ Replace iterative roundUpPow2 calculation with a constant-time bit-twiddling version inspired by “Bit Hacks” – Round up to next power of 2.

O(log(n)) -> O(1)

Checklist

Ensure you completed all of the steps below before submitting your pull request:

• Ran forge fmt?
• Ran forge test?

Pull requests with an incomplete checklist will be thrown out.

[Vectorized]

Does the bytecode size go up or down?

[0xClandestine]

Does the bytecode size go up or down?

@Vectorized MerkleTreeLibTest size increased by 12 bytes after my last commit. Also thinking about it further, there's no need to fully support uint256 values with this approximation, 32 bits would sufficient to support all possible leaves.length values since memory has practical size limits.

[atarpara]

@Vectorized why we don't use ceil(log2 n) = floor(log2(n-1)) + 1 ?

we have optimized formula for a floor(log2 n). Are you worried about bytecode size (is this lib use prod in ethereum)?

[Vectorized]

I can see why this might be needed onchain.

[0xClandestine]

I can see why this might be needed onchain.

I know merkleizeSha256 is needed for beaconchain related proofs and is actively used by EigenLayer.