Feature(profiling-replayer): Implement memory tracking

[danielsn]

What does this PR do?

Adds memory tracking to the profiling-replayer, via a -m or --mem flag.

Motivation

The first step towards optimizing memory is knowing how much we're actually using.

Additional Notes

At least on mac, the reported memory usage seems quite noisy. For two consecuative runs:

Memory usage (kB)
Before adding samples:  102678
After adding samples:   104792  Delta: 2113
After serializing:      119209  Delta: 14417
...
Memory usage (kB)
Before adding samples:  101974
After adding samples:   105332  Delta: 3358
After serializing:      118603  Delta: 13271

How to test the change?

run the profiler as before, but also pass the -m flag.