Nethermind 1.39.3 Mandatory Upgrade Fixes Node Reliability

Nethermind 1.39.3 mandatory upgrade for all node operators. Patch release atop 1.39.2 with reliability fixes in block processing, networking, ABI decoding. Three changes: hardened ABI decode bounds (#12588), fixed pooled-memory leaks (#12034), reduced allocations in EIP-6110 deposit decoding (#12185). Drop-in upgrade, no consensus changes.