fix: deprecate parse, serialize exports for more useful functions

[hf]

parse, serialize from cookie were exported as-is. That's not super useful for importing outside of the library, so they're deprecated and in their stead adding parseCookieHeader, serializeCookieHeader which works with the getAll, setAll cookie methods more ergonomically.

For example, instead of:

getAll() {
  const parsed = parse(request.headers.get('Cookie') ?? '')
  return Object.keys(parsed).map((name) => ({ name, value: parsed[name] }))
}

You can just use:

getAll() {
  return parseCookieHeader(req.headers.get('Cookie') ?? '')
}