perf(icons): cache local asset existence checks

[JustYannicc]

What Changed

• Added a bounded positive cache for local icon/asset existence checks in icon-runtime-assets.tsx.
• Kept negative checks uncached so newly-created extension assets can resolve without waiting for invalidation.
• Added a focused Node test harness for resolveIconSrc that stubs window.electron.statSync and covers extension-relative assets, sc-asset:// URLs, absolute paths, missing assets, configured assetsPath, and the repeated-resolution measurement.

Why

resolveIconSrc was calling window.electron.statSync synchronously every time a local icon or asset source was normalized. List rows, grid cells, and action overlays can all hit this path repeatedly, so resolving the same known-good asset caused repeated sync renderer-to-main IPC/stat work.

Compatibility Impact

• sc-asset://ext-asset URL formatting and local path resolution are unchanged.
• Missing files are intentionally not cached, preserving fallback behavior for assets that appear later.
• Positive results may stay warm until the 4096-entry cache clears. If an asset is deleted after a positive check, the renderer may still emit its sc-asset:// URL until the cache is cleared; this matches the accepted positive-only caching tradeoff for stable extension asset paths.

Metrics

Baseline before code changes, 10,000 resolves of the same stubbed local asset path:

Case	statSync calls	elapsedMs
relative-positive	10,000	18.216
sc-asset-positive	10,000	31.312
absolute-positive	10,000	14.656
relative-negative	10,000	3.197

After change, same 10,000-resolve measurement with a fresh module per case:

Case	statSync calls	elapsedMs
relative-positive	1	15.771
sc-asset-positive	1	33.430
absolute-positive	1	15.359
relative-negative	10,000	5.770

The checked-in focused test also reports: iterations=10000 statSync=1 elapsedMs=14.997.

Checks

• node --test scripts/test-icon-asset-cache.mjs
• pnpm test — 30 passed, 1 skipped live Electron test
• pnpm build:renderer
• pnpm check:i18n — command exited 0; reported existing missing Italian keys settings.ai.whisper.vocabulary and settings.extensions.appSearchScope
• Codex LSP diagnostics on src/renderer/src/raycast-api/icon-runtime-assets.tsx — no errors

Notes / Risks

• A broader LSP scan of src/renderer/src/raycast-api still reports unrelated pre-existing TypeScript diagnostics in context-scope-runtime.ts and hooks/use-cached-promise.ts.
• Full pnpm build was not run because this change is renderer-only and the full build compiles native Swift/addon artifacts; pnpm build:renderer was run for the touched surface.

[JustYannicc]

Superseded by the consolidated renderer performance PR #533: #533. Closing this scoped source PR so review stays centralized there.