Initial commit: Go SRE interview exercises

Includes solved 02-worker-pool and 09-safe-counter (mutex, atomic, sharded).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GbnJj9ZqEx9nUvzkjdwfMq

10-gotchas/ex01-loopvar/main.go

@@ -0,0 +1,20 @@
+// PREDICT the output before running. Then: go run . — and try with an older
+// toolchain mentally: what did this print before Go 1.22?
+package main
+
+import (
+	"fmt"
+	"sync"
+)
+
+func main() {
+	var wg sync.WaitGroup
+	for i := 0; i < 3; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			fmt.Println(i)
+		}()
+	}
+	wg.Wait()
+}