This ticket rewrites timeseries_dynamic_bucket_sizing.js to be more robust and potentially fix BF-30470.

It also documents more thoroughly what the expected behavior of the buckets are in the test as well as cleans up the insertion code, which previously would build up to the bucket size limits iteratively, which potentially introduced the flakiness causing the BF. The test now hits the size limits with a single bulk insertion for both cache pressure and size.