Adjust the decay formula

[gaearon]

This hasn't landed into an @atproto/api release yet but it's a one-liner so I figure we can @ts-ignore and fix later. The actual backend change is already deployed.

This tweaks the ranking formula for Hotness so that replies liked by the thread author (OP) decay a bit slower. In practice, this means that they'll stay closer to the top (but fresh comments will still get their fair chance).

I've considered solutions like bumping the like count by a fixed number, but this doesn't work well for threads of different size. Slowing down the decay exponent ensures that fresh posts still get good visibility, the effect compounds over time, it works for any like counts, and that the boost stays meaningful but not overwhelming.

I also considered strictly prioritizing them above other posts but this disadvantages recent posts too much, leaving no space for them above the fold. Part of the motivation of having hotness was to avoid this.

Overall, the motivation is to give the OP a modicum of curatorial power over the sorting order of the replies below while doing our best to avoid overcorrection due to courtesy likes, missed fresh replies, and inertia.

Test Plan

Jay's post with swords makes for a good example.

In this visualization, red are posts liked by Jay.

Before:

before1.mov

After:

after1.mov

As you can see, recent stuff still squeezes in between them, but OP likes hover higher and are more clumped.

[github-actions]

Old size	New size	Diff
6.96 MB	6.96 MB	127 B (0.00%)

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[gaearon]

nit: we shouldn't use ?: unless there's a good reason for missing key. sometimes missing keys make object shape unstable which makes it harder for JS engines to optimize code