Nimbus v26.6.0 Boosts Pruning and Fixes Stability

Nimbus consensus client v26.6.0 is a medium-urgency release. It improves pruning performance, adds column indexing to light client database, initiates execution client block processing earlier, and caps block data availability at 64 columns during head updates. Fixes include WebSocket reconnection, malformed Era file hardening, and limited column custody crash prevention.