[mlir][Sol] genMemAlloc: zero-init StringType data area for new bytes(N)

[PavelKopyl]

NomicFoundation/solx-solidity#141

[Copilot]

Pull request overview

This PR updates the Sol-to-Yul lowering’s memory allocation helper so that when allocating a memory StringType/bytes with zeroInit=true (e.g., new bytes(N)), the newly allocated data area is explicitly zero-initialized (including padding up to 32-byte alignment).

Changes:

• In evm::Builder::genMemAlloc’s StringType path, round the requested byte length up to a 32-byte multiple for allocation sizing.
• When zeroInit is set, zero the allocated data region via CALLDATACOPY from CALLDATASIZE (out-of-range reads yield zeros).
• Preserve existing behavior for calldata strings ({0,0} null reference) and for the sizeVar-absent case (return zero pointer sentinel).

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[abinavpp]

thank you!