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## Problem We intend for cplane to use the heatmap layer download API to warm up timelines after unarchival. It's tricky for them to recurse in the ancestors, and the current implementation doesn't work well when unarchiving a chain of branches and warming them up. ## Summary of changes * Add a `recurse` flag to the API. When the flag is set, the operation recurses into the parent timeline after the current one is done. * Be resilient to warming up a chain of unarchived branches. Let's say we unarchived `B` and `C` from the `A -> B -> C` branch hierarchy. `B` got unarchived first. We generated the unarchival heatmaps and stash them in `A` and `B`. When `C` unarchived, it dropped it's unarchival heatmap since `A` and `B` already had one. If `C` needed layers from `A` and `B`, it was out of luck. Now, when choosing whether to keep an unarchival heatmap we look at its end LSN. If it's more inclusive than what we currently have, keep it.