alloy-op-evm,kona: cover SDM refund settlement and gas accounting

[nonsense]

Summary

• add a Kona executor test for a successful non-empty SDM PostExec payload
• refund one gas unit from each of eight regular transactions and assert the resulting receipt, gas accounting, balance transfers, and block commitment changes
• make operator_fee_charge return zero before Isthmus before accessing Isthmus-only L1 block fields, with unit-test coverage
• apply SDM refunds after the EIP-7623 calldata floor by discounting both total gas spent and the stored floor gas
• add an alloy-op-evm test that crosses above, at, and below the calldata floor while preserving the native EVM refund and keeping execution-result, block, and receipt gas accounting aligned

Why

The executor tests covered empty PostExec payloads and invalid non-empty payloads, but not successful settlement with non-zero refunds. Exercising that path with the existing pre-Isthmus fixture also exposed that operator-fee calculation could read missing Isthmus-only fields even though operator fees do not exist before Isthmus.

SDM refunds are applied after EVM execution, including after EIP-7623's calldata floor. When a refund lowered canonical gas below that floor, the generic execution-result view remained clamped to the original floor and diverged from canonical block and receipt gas accounting. Discounting the stored floor by the same post-execution refund preserves the intended ordering and keeps all gas views consistent.

Testing

• cargo nextest run --release -p kona-executor
• cargo nextest run --release -p op-revm test_operator_fee_charge_formulas
• cargo nextest run -p alloy-op-evm
• cargo clippy -p alloy-op-evm --all-targets --all-features -- -D warnings
• cargo check -p alloy-op-evm --no-default-features