fix(levm): apply frame transaction gas refunds

[AnkushinDaniil]

Problem

EIP-8141 (Gas refunds) requires EIP-3529 storage refunds to be applied to frame transactions:

gas_used_before_refund = tx_gas_limit - tx_unused_gas
applied_refund = min(refund_counter, gas_used_before_refund // 5)
gas_used = gas_used_before_refund - applied_refund

with the refund counter accumulated across frames and the deltas of reverted frames (or frames unrolled by a failed atomic batch) discarded, and the refund "returned to the gas payer ... and added back to the block gas pool".

ethrex's frame-tx finalization ignored the accumulated refunded_gas counter entirely: the payer was charged for the gross gas used, the coinbase fee was computed on gross gas, and the execution report's gas_used/gas_spent were gross. A frame transaction that clears storage therefore reports a higher gas_used than a conformant client and charges the payer more, which breaks receipt cumulative-gas and block-gas accounting against other clients. gas_refunded in the report was also overloaded to mean "unused frame gas" rather than the EIP-3529 refund.

Change

• Apply applied_refund = min(refunded_gas, total_gas_used / MAX_REFUND_QUOTIENT) at frame-tx finalization; substate checkpoints already discard refund deltas from reverted frames and unrolled batches.
• Charge the payer and pay the coinbase priority fee on the net (post-refund) gas.
• Report gas_used/gas_spent net of the refund and gas_refunded as the applied EIP-3529 refund.

Tests cover: a successful frame netting payer balance, coinbase fee and block gas; refund deltas of a reverted frame discarded; refund deltas of a reverted atomic batch discarded; and the gas_used / 5 cap binding.

Evidence

Commands run on this branch:

cargo check -p ethrex-levm                                  # pass
cargo test -p ethrex-test --test ethrex_tests levm::eip8141_tests
# 79 passed; 0 failed; 0 ignored; 751 filtered out
cargo fmt --all -- --check                                  # pass
git diff --check                                            # pass

Stack

Targets frames-devnet-0. Part of a series of independent EIP-8141 fixes, one PR per logical change, each standing alone against the same base. Siblings: #7040 (canonical low-s), #7043 (recovery id at ecrecover boundary), #7044 (intrinsic gas over payload bytes), #7045 (arbitrary-scheme verification gas), #7047 (frame receipt storage encoding), #7048 (skipped-frame status 2), #7049 (EIP-7623 calldata floor).

Consensus risk / limits

Consensus-affecting: it changes gas_used (receipts, cumulative gas, block gas accounting) and payer/coinbase balances for any frame transaction that accrues EIP-3529 refunds. Covered by unit tests only; no cross-client conformance fixture yet.

[edg-l]

Superseded by #7004: frame-tx finalization on main applies refunded_gas capped at total_gas_used / MAX_REFUND_QUOTIENT and reports gas_used, gas_spent and gas_refunded accordingly. Main's existing frame-tx refund tests cover this behaviour. Closing as fixed; thanks.