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/ex03-closed-channel/main.go

@@ -0,0 +1,14 @@
+// PREDICT each printed line, and what the last statement does.
+package main
+
+import "fmt"
+
+func main() {
+	ch := make(chan int, 2)
+	ch <- 1
+	close(ch)
+	fmt.Println(<-ch)
+	v, ok := <-ch
+	fmt.Println(v, ok)
+	close(ch) // ???
+}