Benchmark memory

[tayloraswift]

this PR adds hard memory consumption benchmarks to validate the absolute minimum RAM needed to use the Firewall, which is currently about 160 MB. this figure makes a lot of sense, the Firewall itself is about 63 MB, and we need to copy the buffer once in order to turn Foundation.Data into [UInt8], which would transiently use 126 MB of RAM. the remaining memory can be attributed to the test application itself, and its linked libraries:

     63 MB — Used by IP.Firewall itself
     63 MB — Used by Foundation.Data (would not appear in production)
     34 MB — Used by the test application, including the Swift stdlib
    2.6 MB — libstdc++.so.6
    2.1 MB — libc.so.6
    1.0 MB — libm.so.6
+   0.2 MB — libgcc_s.so.1
——————————
    165 MB

i guess the C/C++ libraries get loaded lazily, which is why the benchmark squeaks by with 160 MB of RAM and no swap.