BuilderNet Proposes Sponsored Bundles to Fix Gas Funding Failures

BuilderNet proposes sponsored bundles via `eth_sendBundle`, matching Titan and Quasar. When a tx fails with LackOfFundForGasLimit, the builder injects funding. Inclusion requires builder balance after ≥ before minus sponsored gas, preserving the no-loss invariant. Value arrives inside the bundle; senders skip running an EOA.