chore: upgrade Svelte submodule to 5.57.0

[github-actions]

Starter PR to upgrade the Svelte compatibility target.

• from: 5.56.10
• to: 5.57.0 (7bc0a70fe64d)

⚠️ Not mergeable as-is

A svelte bump needs fixtures regenerated and any regressions
fixed. CI will fail until that is done. To finish:

1. git fetch origin chore/upgrade-svelte-5.57.0 && git checkout chore/upgrade-svelte-5.57.0
2. git submodule update --init --recursive submodules/svelte
3. Run the upgrade-svelte skill (or ./scripts/dev/upgrade-svelte.sh 5.57.0)
   to rebuild the compiler, regenerate fixtures, fix regressions,
   refresh docs, and add a changeset.
4. Push the fixes to this branch.

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Release notes

Minor Changes

• feat: export RenderOutput, SyncRenderOutput, Csp and Sha256Source from svelte/server (#18648)

• feat: add has function to createContext (#18472)

• feat: support defaultValue on <select> (#18591)

• feat: add getOrInsert/getOrInsertComputed to SvelteMap (#18728)

Patch Changes

• fix: block template store subscriptions on the promise that assigns the store (#18582)

• fix: route $derived teardown errors through invoke_error_boundary (#18486)

• fix: track SvelteDate snapshots in reactions (#18700)

• fix: remove <svelte:head> anchors on unmount (#18697)

• fix: warn on undeclared shorthand event handlers on <svelte:window>, <svelte:document> and <svelte:body> (#18480)

• perf: reuse the cached value in the <option>/<select> value guard (#18713)

• fix: prevent malformed AST output for <select> with static value attribute (#18449)

• fix: apply ownership mutation ignores to binding assignments (#18718)

• fix: prevent onoutroend from firing twice when compilerOptions.hmr is true (#18655)

• fix: preserve whitespace after inline elements when printing (#18685)

• perf: fold SSR block-open markers into the branch's first push (#18712)

• fix: run onDestroy callbacks when a server render throws (#18585)

• fix: report derived_invalid_export for export let x = $derived(...) in runes mode (#18692)

• fix: never apply class hash to elements inside <svelte:head> (#18160)

• fix: keep defaultChecked on hydrated radio inputs with spread attributes (#18701)

• fix: accept onfocusin/onfocusout in a11y_mouse_events_have_key_events (#18689)

• perf: O(n²)→O(n) Map lookups for legacy $: reactive statement ordering (#18602)

• fix: distinct memoizer on style/class directives (#18466)

• fix: measure nested transitions before applying their starting styles (#18647)

• fix: don't turn component instances stored in $state into state proxies (#18646)

• perf: emit $.only_child for elements with a single child (#18717)

• fix: omit bind:focused from SSR output (it has no HTML attribute) (#18724)

• fix: more robust rendering of Svelte custom element slots (#18710)

• perf: optimize simple object destructuring in @const tags (#18390)

• fix: properly apply static textarea value attribute during CSR (#18727)

• fix: end a restored reaction context at the end of its synchronous segment (#18694)

• fix: keep the dependencies of a reaction that throws, so deriveds it read are neither leaked nor stuck in their error (#18703)

• fix: don't resurrect outroing elements when an ancestor block is paused and resumed (#18431)

• perf: use $.comment() for single-comment templates (#18714)

• chore: move @types/trusted-types to devDependencies (#18730)

• perf: store setters cache as Set instead of Array (#18251)

• fix: transform derived assignments and select function bindings correctly during server-side rendering (#18669)

• fix: keep boolean attributes with an empty string value when rendering attribute objects on the server (#18721)

• fix: sync SvelteURL port signal when the protocol setter clears the port (#18705)

• fix: block declaration tags and {@const} on async values read inside closures (#18533)

• fix: avoid css tree-shaking for exported Snippet (#18540)

• perf: treat <img loading> as a static element again (#18711)

• fix: prevent selectedcontent mutation from changing the selected option (#18495)

• fix: avoid NaN keyframe values in slide transition for elements without a layout box (#18430)

• fix: preserve line feed character references in attribute values (#18691)

• fix: decode uppercase-X hex numeric character references (&#X...;) (#18708)

• chore: clarify when $effect.pre runs relative to DOM updates (#18534)

• fix: scope SSR boundary failed snippets to their boundary (#18593)

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Opened by the auto-update-svelte workflow.

[baseballyama]

Superseded by #4401, which bumps the submodule together with the 40 compiler-side ports 5.57.0 needs.