introduce memory usage benchmarks for Rust-based frameworks

[eightfilms]

In private conversations with @tumberger we discussed 2 ways of measuring memory usage:

1. in-language memory benchmarks: this would require most likely require usage of jemalloc, which means we need to depend on libc directly.

2. external tools: we could also use /usr/bin/time or something like valgrind.

If we decide on 2), the logic between the test runner<>benchmarks would have to be separated, since in the current runner we are doing other tasks like writing to CSV, etc. which means we may not get the most accurate results.

[StefanosChaliasos]

We will probably need to go with the second option so that we can use the same tooling across all frameworks. Hence, we will need separate runners per phase.

[StefanosChaliasos]

In #32, we use time to perform the measurement.