Speed up @cachedList

[erikjohnston]

This speeds things up by ~2x.

The vast majority of the time is now spent in LruCache moving things around the linked lists.

We do this via two things:

1. Don't create a deferred per-key during bulk set operations in DeferredCache. Instead, only create them if a subsequent caller asks for the key.
2. Add a bulk lookup API to DeferredCache rather than use a loop.

Reviewable commit-by-commit.

[reivilibre]

Looks good overall, mostly just naming concerns to make it easier to follow for us noobs

[MadLittleMods]

Great progress @erikjohnston 🎉

Here are the before/after timings for this PR using the have_seen_events benchmark from #13561

# events	Before	After
50k	. Benchmark time (1 cold cache ): 3.7170820236206055 Benchmark time (2, warm cache): 0.2985079288482666 Benchmark time (3, warm cache): 0.28847789764404297 Benchmark time (4, odds ): 0.1537461280822754 Benchmark time (5, odds ): 0.14780497550964355 Benchmark time (6, evens ): 0.1475691795349121 Benchmark time (7, evens ): 0.14868617057800293	. Benchmark time (1 cold cache ): 1.062384843826294 Benchmark time (2, warm cache): 0.18310809135437012 Benchmark time (3, warm cache): 0.17781400680541992 Benchmark time (4, odds ): 0.09939789772033691 Benchmark time (5, odds ): 0.09195113182067871 Benchmark time (6, evens ): 0.08882665634155273 Benchmark time (7, evens ): 0.08661413192749023
100k	. Benchmark time (1 cold cache ): 8.10055136680603 Benchmark time (2, warm cache): 0.6121761798858643 Benchmark time (3, warm cache): 0.6093218326568604 Benchmark time (4, odds ): 0.29950785636901855 Benchmark time (5, odds ): 0.3049640655517578 Benchmark time (6, evens ): 0.3025388717651367 Benchmark time (7, evens ): 0.29833483695983887	. Benchmark time (1 cold cache ): 2.264657735824585 Benchmark time (2, warm cache): 0.3539161682128906 Benchmark time (3, warm cache): 0.3556997776031494 Benchmark time (4, odds ): 0.17580008506774902 Benchmark time (5, odds ): 0.17888712882995605 Benchmark time (6, evens ): 0.1756150722503662 Benchmark time (7, evens ): 0.17418384552001953
200k	. Benchmark time (1 cold cache ): 19.106724977493286 Benchmark time (2, warm cache): 22.98161005973816 Benchmark time (3, warm cache): 23.126408100128174 Benchmark time (4, odds ): 11.401129007339478 Benchmark time (5, odds ): 0.6159579753875732 Benchmark time (6, evens ): 12.087002992630005 Benchmark time (7, evens ): 0.6241748332977295	. Benchmark time (1 cold cache ): 4.827088117599487 Benchmark time (2, warm cache): 4.958348035812378 Benchmark time (3, warm cache): 4.923892974853516 Benchmark time (4, odds ): 2.5139119625091553 Benchmark time (5, odds ): 0.3530576229095459 Benchmark time (6, evens ): 2.465486764907837 Benchmark time (7, evens ): 0.3511021137237549