Remove status setters, and use a new response.notFound() method.

[jplhomer]

Description

Fixes #1488

We originally replaced HydrogenResponse.writeHead() with set status(value() in #1433. However, we can't reliably override the status and statusText properties of the Response class we're extending, because the implementation on some hosting runtimes like Cloudflare explicitly forbids it.

This PR adds a new HydrogenResponse.notFound() method which developers can use to declare a 404 when inside an server component.

Additional context

I don't anticipate developers needing to set custom response codes inside server components, so I think the removal of a custom status setter is an acceptable tradeoff.

Note that it is still possible to return a completely custom Response from API functions, where a custom status can be provided in the initial options:

export async function api() {
  return new Response('foo', { status: 201 });
}

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• Read the Contributing Guidelines
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123)
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[frandiox]

Alternative to writable status in CFW here: Shopify/hydrogen#1504

[jplhomer]

Gonna close in favor of that one!