chore: upgrade to vitest 5

[rexxars]

…also the latest playwright, oxfmt, oxlint, happy-dom and switches to the new cloudflare vitest plugin instead of the worker pool.

[Copilot]

🔵 Needs a closer look

The major test-runner migration spans several runtimes and requires successful CI validation across their integrations.

0 open findings

What changed in this PR

Upgrades Vitest and related test tooling while migrating workerd tests to Cloudflare’s new plugin.

Changes:

• Upgrades Vitest, Playwright, happy-dom, Oxc tools, and parser dependencies.
• Migrates browser/workerd configuration to updated APIs.
• Stabilizes an event-property test and ignores Vitest’s cache.

File	Description
vitest.workerd.config.ts	Migrates to the Cloudflare plugin and disables filesystem module caching.
vitest.ios.config.ts	Moves the API server configuration for Vitest 5.
vitest.browser.config.ts	Moves browser API configuration for Vitest 5.
test/​client.test.ts	Prevents buffered events from racing the assertion.
package.json	Upgrades test tooling and parser dependencies.
deno.lock	Updates Deno dependency resolutions.
bun.lock	Updates Bun dependency resolutions.
.gitignore	Ignores Vitest cache output.

🧠 Review effort: Balanced

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