fix: stop currentTime binding updates during outros

[svelte-triage-bot]

Fixes #15053.

The currentTime binding's RAF/event callback continued writing after its owning branch effect became inert during an outro. If the binding targeted a property on the condition value, that value could already be null, producing Cannot set properties of null.

This captures the binding's owning effect and skips media-to-state writes while that effect is inert. A reduced transition-media-binding-outro runtime-runes sample reproduces the failure by dispatching timeupdate while the audio element is outroing.

Verification:

• Reduced test failed before the patch with Cannot set properties of null (setting 'currentTime') and passes after it.
• pnpm test runtime-runes: 2660 passed, 47 skipped.

Self-review found and fixed an effect typing issue; no remaining blocking or worth-fixing findings.

[pkg-svelte-dev]

Install the latest version of svelte from b2a6c0c:

pnpm add https://pkg.svelte.dev/svelte/c/b2a6c0c9f93df27bee38ac31b41bb381a5c6e822

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18642

[changeset-bot]

⚠️ No Changeset found

Latest commit: b2a6c0c

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-18642-svelte.vercel.app/