search: simplify event loop

Created by: camdencheek

Just a small refactor to simplify the main streaming event loop to make it more clear what the exit conditions are, etc.

• Pulls event handling into a closure
• Simplifies the for/select loop to keep variables scoped
• Inlines matchesAppend because it is a single-line closure used in one place

cc @keegancsmith @stefanhengl