asyncio.streamreader sizing for dispatch_checks.py

Effecting ability to accurately output logs - implementing patch by logging "oversized line" for now requires further investigation #48433 aka logging the oversized line, not implementing to not block storage any further rn

Start by locating dispatch_checks.py and tracing how its asyncio.StreamReader sizing affects log output and storage blocking. Reproduce the oversized-line case, clarify the intended logging behavior from issue #48433, and add or update tests that demonstrate the issue is resolved without blocking storage.

Written by the indexing model from the issue text.