Add option to nest `useOpenTelemetry` resolver spans by field path

Is your feature request related to a problem? Please describe.

Currently every resolver span created by useOpenTelemetry({ resolvers: true }) gets parented directly under the top-level operation span, regardless of how deep the field actually is in the query.

So for something like:

query {
  user(id: "1") {
    posts {
      comments {
        author { name }
      }
    }
  }
}

User.posts, Post.comments, Comment.author, and Author.name all end up as direct siblings under query, instead of a chain that reflects the actual resolution tree.

The old @opentelemetry/instrumentation-graphql defaults to tree-shaped nesting, with a config flag called flatResolveSpans to opt out into flat behavior. They achieved this by tracking spans in a map keyed by the field's info.path, and walking that path backwards to find the nearest ancestor that already had a span.

Describe the solution you'd like

An option to enable tree-shaped nested spans.