Address review: use slices.Clone, simplify concurrent test

- Replace manual make+copy with slices.Clone in Snapshot()
- Remove redundant _ = len(data); Snapshot() call alone is
  sufficient to exercise the lock under -race

mtglib/internal/doppel/scout_conn_collected.go

 package doppel
 
 import (
+	"slices"
 	"sync"
 	"time"
 )
 // Snapshot returns a copy of the collected data and the write index.
 func (s *ScoutConnCollected) Snapshot() ([]ScoutConnResult, int) {
 	s.mu.Lock()
-	snapshot := make([]ScoutConnResult, len(s.data))
-	copy(snapshot, s.data)
+	snapshot := slices.Clone(s.data)
 	writeIndex := s.writeIndex
 	s.mu.Unlock()
 

mtglib/internal/doppel/scout_conn_collected_test.go

 		defer wg.Done()
 
 		for i := 0; i < 1000; i++ {
-			data, _ := collected.Snapshot()
-			_ = len(data)
+			// call Snapshot concurrently to exercise the lock under -race
+			collected.Snapshot() //nolint:errcheck
 		}
 	}()