Add performance tests to measure baselines about datamapper HOT 2 OPEN

INSERTS: cost of datamapper adds: 4.31% extra on top of EF insert cost.

500 inserts
Performance add datamapper time to complete:54.426113
Performance add raw time to complete:52.2669895
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0.108852226 secs per datamapper insert
0.104533979 secs per raw ef insert

0.004318247 secs extra cost per insert on my machine (not a good metric, relative sizing more important)
4.131% extra cost per insert. Not bad at all IMO.

from datamapper.

500 updates (insert then delete child repeated)
Performance update datamapper time to complete:13.0977492
Performance update raw time to complete:11.7436717
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0.0261954984 secs per datamapper update
0.0234873434 secs per ef update

0.002708155 secs extra cost per update
11.53% extra cost per update.

from datamapper.