Preserve historical withdrawal accounting on Drivenet

[ekulkisnek]

Problem

Commit 48208c5 correctly made new withdrawals fund both the payout and mainchain fee, but Drivenet already contained blocks mined under the former payout-only rule. Current nodes stop syncing when they revalidate those blocks.

Fix

• keep the corrected rule for every new block
• apply payout-only accounting only to the two observed historical block hashes
• use the same rule for fee validation and the fee-committing Merkle root
• add focused tests for historical acceptance and current underfunding rejection

Evidence

Before this change, replay stopped at height 447 on block f9a7a9117bec4ed6c4fffbf3b651b60f9459a5fc881f267b271778874ad55d0f. A second historical block was found at height 807: 208e6bb567efd46d073bab68d9cff041279faada60c7f27a011a56bd1f7f86b7. With both exact exceptions, the node replayed the existing Drivenet history to tip height 7360.

Validation: cargo test --workspace --locked, cargo clippy --workspace --all-targets --locked -- -D warnings, formatting, and diff checks pass.