test: add hash/maphash demo test case

Add test case in _demo/go/maphash to verify hash/maphash functionality
with the new runtime.rand and runtime.memhash support.

Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <luoliwoshang@users.noreply.github.com>
Co-authored-by: xgopilot <noreply@goplus.org>

_demo/go/maphash/maphash.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"fmt"
+	"hash/maphash"
+)
+
+func main() {
+	var h maphash.Hash
+	h.WriteString("hello")
+	fmt.Printf("0x%x\n", h.Sum64())
+
+	h.Reset()
+	h.WriteString("world")
+	fmt.Printf("0x%x\n", h.Sum64())
+
+	h.Reset()
+	h.WriteString("test")
+	v1 := h.Sum64()
+
+	h.Reset()
+	h.WriteString("test")
+	v2 := h.Sum64()
+
+	fmt.Printf("0x%x == 0x%x\n", v1, v2)
+}