Limit cache growth for rolling time ranges

[rosenrot00]

• keep automatic rolling views limited to their current visible time range
• return and retain only cached data needed by active traces
• preserve the leading boundary value used to draw continuous state history
• combine retention ranges for traces that share an entity but use different time offsets
• remove cache entries for entities no longer configured
• avoid pruning live states that arrive while a history request is in flight
• fix compacting nested cached ranges so an enclosing range is not shortened

The observed range previously grew for the full lifetime of a browser tab. The cache was never pruned, so every refresh copied, transformed, sorted, and filtered all points loaded since the tab was opened. CPU and memory usage therefore increased over time even when the graph only displayed a fixed rolling window.