Move partial state CLI flags into their own "PARTIAL STATE" help category
(matching BEACON CHAIN, DEVELOPER CHAIN patterns), improve Usage strings
with examples and constraint descriptions, expand PartialStateConfig doc
comments to explain EIP-7928 implications, and raise BAL retention minimum
from 64 to 256 (required by BLOCKHASH opcode).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>