use 1/998 for swap rows rather than 4/9

[leeoniya]

@krausest

i did a bit of testing as a followup to #305 (comment)

dunno if you wanna sneak this change into Round 7, but the results are rather revealing:

[leeoniya]

the plot thickens...

apparently some libs are micro-optimized only for leading/trailing swapping rather than general swappage. so when we switch to 1/998 instead of 0/999, we get to see prettier autumn colors:

[krausest]

Will run the swap benchmark and post results this evening.

[krausest]

Here they are.

[leeoniya]

hmm, is choo v6.5.0-keyed misclassified?

[krausest]

Thanks for spotting it. At least its naming was already correct...
Fixed in ee308dc