Nethermind 1.38.1 Patches OP Karst, Refreshes Superchain Registry

Nethermind 1.38.1 patch adds OP Karst fork, refreshes Superchain registry, removes bundled Base mainnet/sepolia configs. 5 OP Stack changes. Base operators must supply own chainspec. Engine API V4 gated behind OP Isthmus. Breaking: arena-z, swell-mainnet removed.