Draft: Fix crash when FMU lacks centralEnergyPlant (e.g. lassen)

Brewer, Wesrequested to merge
fix/lassen-cooling-crash into main

Guard CEP data extraction with a key check so systems whose FMU does not output a centralEnergyPlant component can still run with cooling enabled, producing CDU data but an empty CEP list.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

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