The `threeDecimalPlaces` helper using `number.toFixed(3)` allowed for
a maximum difference of 0.001 for a pair like 0.0005 / 0.00149999, but
had no lower limit on the difference, a pair like 0.0004999 / 0.0005
would fail.

This may be the cause of a Safari failure `!EQ(6.548, 6.549)`:
https://wpt.fyi/results/media-source/mediasource-endofstream.html?run_id=255090001