batch invalidations

[tombl]

...in a microtask.

makes invalidate async, so while it's less convenient, you can still await or .then for your post-update DOM handling needs.

good for perf but mainly because I've just discovered a pile of reentrancy issues and don't want to keep hunting for them individually.

note that most usages in the examples didn't even need updating because very few actually need this. this does probably break all the benchmarks though.

closes #200

[github-actions]

Size Change: +16 B (+0.47%)

Total Size: 3.45 kB

Filename	Size	Change
./dist/client.min.js	2.06 kB	+15 B (+0.73%)
./dist/shared.min.js	566 B	+1 B (+0.18%)

ℹ️ View Unchanged

Filename	Size
./dist/index.min.js	63 B
./dist/server.min.js	762 B

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