Lighthouse v8.2.1 Fixes Security Flaws, Urges Beacon Node Upgrade

Lighthouse v8.2.1 fixes security vulnerabilities and partial data column bugs; all mainnet beacon node users should upgrade. Staking users face high priority for beacon nodes. Fixes optimize proposer preparation and cached data handling. Hoodi/Sepolia users can disable with --enable-partial-columns false. Data column backfill OOM known issue, fixed in v8.3.0.