Update 10/22/20
Forgot to mention in my last update that I also dosed a bottle of Dr. Tim's One and Only on 10/20 in the hopes of 1) accelerating the cycle and 2) seeding a more diverse bacterial population in the tank.
Still no definitive movement on the nitrite front. Given I only use the nitrite test when a tank is cycling, I don't like uncertainty, and I wanted to get a better read on my nitrites than, "Maybe purple?", I did a dilution curve test: pure tank water, 1:1 tank water to RODI water, and 1:3 tank water to RODI water. Based on these tests, it looks like the tank is right at ~1 ppm nitrite so it seems to be going down slowly, but surely.
Curiosity got the better of me, so I spent some time reading to try and figure out why my cycle might be progressing so slowly. The answers that I got were high salinity (my tank has been at 1.024), extremely high nitrites (not the case), low temperature (I've had the tank at 81°F to encourage faster bacterial division), low pH (holding steady at 7.8) and phosphate block. That last one interested me because 1) phosphate is an essential component of the backbone of DNA, 2) DNA replication is necessary for bacterial replication, and 3) I had no phosphate source at the start of my cycle. So to satisfy my own curiosity I ghost fed the tank with some reef roids given its phosphate content, and its small particulate size lending to a more rapid breakdown than ghost feeding with shrimp/pellets.
Fingers crossed the cycle will finish soon!