Search backend: remove stream from searchResolver

Created by: camdencheek

This does a few things, split up into separate commits:

1. It uses the new SearchClient for the compute streaming endpoint
2. Now that no streaming clients use searchResolver, we can remove stream from the search args and inline resultsBatch, removing resultsStream.
3. Since we only care about whether we're streaming or not during planning phase (we just check if stream is nil or not), we can just pass a protocol into the Plan() function.

Stacked on #31786

Test plan

Covered by integration tests and briefly manually tested. It was unclear to me whether there are any tests covering streaming compute, so lemme know if I should test that manually.