When all endpoints are non-ready (ready=false, serving=false, terminating=false),
the topologyModeFromHints function was incorrectly logging "Ignoring same-zone
topology hints for service since no hints were provided for zone" because the
boolean flags remained at their initial values after the loop skipped all
non-ready endpoints.
This fix adds tracking for whether any ready endpoints were processed and
returns early if none exist, avoiding misleading log messages.
Also adds a test case covering this scenario.
18f56fa7c7