Besu 26.6.0 Requires JDK 25, Deprecates PoW

Besu 26.6.0 released; requires JDK 25+. RPC block numbers and hashes now reject non-hex values. Proof of Work consensus deprecated. Parallelized block body lookups cut latency for engine_getPayloadBodiesBy* calls. Added eth_baseFee and eth_getStorageValues RPCs. Fixed debug_accountAt off-by-one, Address.addressHash() stalling, and transaction pool restore. BFT legacy encoding flag needed for 25.x upgrades.