pad transaction signature values to equal 32 bytes

[luu-alex]

Coming from the PR comments #6033 (comment) The rpc method getblock test fails due to transaction signature value r sometimes returning less than 32 bytes. this needs to be padded so it passes byte32 validation
https://github.com/web3/web3.js/blob/4.x/packages/web3-eth/test/integration/block/rpc.getBlock.test.ts

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