net-rs: switch net-node to jemalloc allocator
glibc's allocator holds freed pages on its freelist and returns them to the OS lazily, inflating RSS under heavy small-allocation churn. At 50 TPS the cluster grew to ~10 GB with glibc but ~7 GB with jemalloc — a ~30% reduction with no other change. tikv-jemallocator is the standard Rust binding and is already used by other Cardano-adjacent tools. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>