Per-tx gas-dimension snapshot captured at the block-execution boundary.
All fields are pre-refund except gas_spent and gas_refunded which are
the user-pays (post-refund) values.
Emit a structured per-tx gas-dimension dump. Called from the block-validation
site when block_gas_used disagrees with header.gas_used. If breakdowns is
empty (paths that don’t populate it, e.g. L2 producer), a one-liner is logged.