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## Problem There's no efficient way of querying the layer map for a range. ## Summary of changes Introduce a range query for the layer map (`LayerMap::range_search`). There's two broad steps to it: 1. Find all coverage changes for layers that intersect the queried range (see `LayerCoverage::range_overlaps`). The slightly tricky part is dealing with the start of the range. We can either be aligned with a layer or not and we need to treat these cases differently. 2. Iterate over the coverage changes and collect the result. For this we use a two pointer approach: the trailing pointer tracks the start of the current range (current location in the key space) and the forward pointer tracks the next coverage change. Plugging the range search into the read path is deferred to a future PR. ## Performance I adapted the layer map benchmarks on a local branch. Range searches are between 2x and 2.5x slower than point searches. That's in line with what I expected since we query thelayer map twice. Since `Timeline::get` will proxy to `Timeline::get_vectored` we can special case the one element layer map range search at that point.