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/ex04-nil-select/main.go

@@ -0,0 +1,16 @@
+// PREDICT: which case fires? What if b were nil too?
+package main
+
+import "fmt"
+
+func main() {
+	var a chan int // nil
+	b := make(chan int, 1)
+	b <- 42
+	select {
+	case v := <-a:
+		fmt.Println("a", v)
+	case v := <-b:
+		fmt.Println("b", v)
+	}
+}