Stop interacting with the SD card from the scan core

[JosephHewitt]

Benchmarks show that each logged WiFi network on side A takes ~21ms for the printf to the file object. The flush afterwards is ~8ms. The times have quite some jitter, but this seems to be about the average.

Worst case I have seen so far is ~40ms to write a single new network then flush. Since the WiFi scan part of the loop is ~1430ms (110ms per channel x 13 channels), we're wasting around 3% of the scan core on flushing out the data -- and that's if only a single new network is found. This slowdown will compound with more new networks found in a single channel scan.

Moving the writing to the other core will definitely see an increase in scan performance, but it may not be able to keep up. This will need very close monitoring after implementing, especially in extremely high WiFi dense areas.

It might be worth creating another xTaskCreatePinnedToCore for write operations which has a higher priority that simply yields when there is nothing to write.