[v1.0] pass `request-options` to `outgoing-handler` by `borrow`

In 0.2, outgoing-handler gets passed an option<request-options>:

  @since(version = 0.2.0)
  handle: func(
    request: outgoing-request,
    options: option<request-options>
  ) -> result<future-incoming-response, error-code>;

It would be nice if this was instead an option<borrow<request-options>> so that the same options could be reused across many requests.

We can't change this in 0.2 because it would be a breaking change, but we should take the opportunity to fix it in 0.3.

The issue identifies the outgoing-handler WIT definition and the request-options type, but names no file or test path. Start by locating the v0.3 interface definition and reviewing how borrowed request-options values are represented. Done means the v0.3 API passes reusable borrowed options while preserving the existing 0.2 signature.