memory test for brand=phet (1.2 branch)

[pixelzoom]

This is a memory test for brand=phet, prior to creating the 1.2 branch. The previous test was in #190.

There are 2 test procedures:

(1) Standard fuzz test

1. Take a heap snapshot at startup.
2. Run with ?fuzz for 10 minutes, taking snapshots at 1-minute intervals.
3. Take a heap snapshot at t=15 minutes.

(2) Heap snapshots every 100 generations

1. Run the sim with secondsPerGeneration=0.25 (so this test can be done quickly)
2. Go to the Lab screen
3. In the "Add Mutations" panel, press the dominant buttons for Fur, Ears, Teeth (so that we create a lot of points on the Population graph)
4. In the "Environmental Factors" panel, check the "Limited Food" checkbox (so that the population stabilizes)
5. In the Population graph, zoom out to y-axis range 0-500 (so that we create the view for plots)
6. Take a heap snapshot at Generation 0
7. Press the "Add a Mate" button
8. Take a heap snapshot every ~100 generations, including generation 1000. Heap size should be similar for each of these snapshots.
9. Close the "Memory Limit" dialog that pops up at Generation 1000.
10. Press the "Reset All" button, then take another Generation 0 heap snapshot. Heap size should be similar to the heap size in step 6.

[pixelzoom]

Test configuration: MacBookPro16,1, Chrome 85.0.4183.102, Incognito

(1) Standard fuzz test
https://phet-dev.colorado.edu/html/natural-selection/1.2.0-dev.4/phet/natural-selection_en_phet.html?fuzz

Time (minutes)	Heap Size (MB)
0	24.8
1	28.6
2	29.9
3	30.2
4	30.3
5	30.7
6	30.9
7	30.8
8	31.1
9	31.2
10	31.2
15	32.0

(2) Heap snapshots every 100 generations
https://phet-dev.colorado.edu/html/natural-selection/1.2.0-dev.4/phet/natural-selection_en_phet.html?secondsPerGeneration=0.25

Generation	Heap Size (MB)
0	24.9
100	42.1
200	42.6
300	42.7
400	42.4
500	42.5
600	42.5
700	43.0
800	42.4
900	43.0
1000	42.4
0	26.7

All of the above looks great. I'll keep this issue open for QA to confirm during RC testing for #208.

[pixelzoom]

Removing "ready-of-qa" label because PhET brand will not be tested in the 1.2 branch.

When we start the next phase of deployment, it will be for both brands in a new 1.3 branch, and another round of memory testing will be needed.