Update columnar; introduce mimalloc

Author: frankmcsherry

differential-dataflow/Cargo.toml

@@ -21,6 +21,7 @@ rand="0.4"
 itertools="^0.13"
 graph_map = "0.1"
 bytemuck = "1.18.0"
+mimalloc = "0.1.48"
 
 [dependencies]
 columnar = { workspace = true }