Buffer stderr/stdout until newlines to improve path extraction
Buffer stderr/stdout until newlines to improve path extraction

This should fix flaky tests where paths aren't detected because (on slow CI machines?) the lines arrive in multiple chunks. This could result in messages not getting to the client if they're not terminated with newlines but seems unavoidable if we want to map these paths.

Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code