Add memory benchmarks

[jeremykubica]

Add a pair of memory benchmarks for the learning loop (one using RandomForest and one for KNN)

[github-actions]

Before [06c1a25]	After [ca07729]	Ratio	Benchmark (Parameter)
failed	failed	n/a	benchmarks.peakmem_learn_loop('KNN')
failed	failed	n/a	benchmarks.peakmem_learn_loop('RandomForest')
138±0.6ms	137±2ms	1.00	benchmarks.time_feature_creation
2.66±0.01s	2.67±0.01s	1.00	benchmarks.time_learn_loop('RandomForest', 'RandomSampling')
2.65±0.01s	2.66±0.02s	1.00	benchmarks.time_learn_loop('RandomForest', 'UncSampling')
174±3ms	172±2ms	0.99	benchmarks.time_learn_loop('KNN', 'RandomSampling')
176±0.8ms	173±2ms	0.98	benchmarks.time_learn_loop('KNN', 'UncSampling')

Click here to view all benchmarks.

[drewoldag]

So quick. Thanks!