Add task time estimates (time_per_day, time_per_instance) to all 88 datasets (part 2)

Update datasets: AEI v6 censored-pct fill; add AEI eco2015/eco2025 bucket series; remove superseded aei_*_usage files (part 2)

Add AEI v6.1/v6.2 (June 2026 release): 12 new v6-era datasets, supplementary builds moved to 2026-05-31, remove stale task-properties variant; full refresh of regenerated datasets