Proposal: Implement Vue-style effect cleanups

[jviide]

This pull request suggest the following middle point between having and not havig autodisposed effects. It also modifies effect cleanups introduced in #183, allowing scheduling multiple effect cleanups during the same effect run:

import { signal, effect } from "@preact/signals-core";

effect((cleanup) => {
  cleanup(() => {
    console.log("this will run the next time the effect rerun or disposed");
  });
  cleanup(() => {
    console.log("ditto");
  });
});

Effects aren't parented to their contexts by default anymore, and there is no autodisposal. It's pretty easy to achieve a similar effect:

import { signal, effect } from "@preact/signals-core";

effect((cleanup) => {
  cleanup(effect(() => {
    console.log("this effect will be autodisposed, sort of");
  }));
});

This version avoids autodisposal's "spooky action by distance" (accidentally binding an effect's lifetime to another one) by making the disposals explicit, while getting most of autodisposal's benefits. It also requires a bit less code 🙂

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Latest commit: b1f1ba9

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Size Change: +257 B (0%)

Total Size: 67.7 kB

Filename	Size	Change
docs/dist/assets/index.********.js	1.08 kB	+247 B (+30%)	🚨
docs/dist/assets/signals-core.module.********.js	1.39 kB	-13 B (-1%)
docs/dist/assets/signals.module.********.js	1.96 kB	+1 B (0%)
docs/dist/basic-********.js	245 B	+1 B (0%)
docs/dist/demos-********.js	3.35 kB	+3 B (0%)
docs/dist/nesting-********.js	1.13 kB	-1 B (0%)
docs/dist/react-********.js	239 B	-1 B (0%)
packages/core/dist/signals-core.js	1.44 kB	-18 B (-1%)
packages/core/dist/signals-core.mjs	1.46 kB	-22 B (-1%)
packages/preact/dist/signals.js	1.2 kB	+13 B (+1%)
packages/preact/dist/signals.mjs	1.17 kB	+14 B (+1%)
packages/react/dist/signals.js	847 B	+14 B (+2%)
packages/react/dist/signals.mjs	829 B	+19 B (+2%)

ℹ️ View Unchanged

Filename	Size
docs/dist/assets/client.********.js	45.8 kB
docs/dist/assets/jsxRuntime.module.********.js	282 B
docs/dist/assets/preact.module.********.js	4 kB
docs/dist/assets/style.********.js	21 B
docs/dist/assets/style.********.css	1.21 kB

_{compressed-size-action}

[jviide]

Based on Slack discussion we won't be going with this approach for now. Superceded by #191.