add nn-cli example (#4373)

an example application with flexible cli options which
aims to allow us to perform any wasi-nn operations.

eg.
```
--load-graph=file=fixture/model.xml,file=fixture/model.bin,id=graph
--init-execution-context=graph-id=graph,id=ctx
--set-input=file=fixture/tensor.bgr,context-id=ctx,dim=1,dim=3,dim=224,dim=224
--compute=context-id=ctx
--get-output=context-id=ctx,file=output.bin
```

wamr-wasi-extensions/samples/nn-cli/fileio.c

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2025 Midokura Japan KK.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+/*
+ * modified copy-and-paste from:
+ * https://github.com/yamt/toywasm/blob/0eaad8cacd0cc7692946ff19b25994f106113be8/lib/fileio.c
+ */
+
+#include <sys/stat.h>
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "fileio.h"
+
+int
+map_file(const char *path, void **pp, size_t *sizep)
+{
+    void *p;
+    size_t size;
+    ssize_t ssz;
+    int fd;
+    int ret;
+
+    fd = open(path, O_RDONLY);
+    if (fd == -1) {
+        ret = errno;
+        assert(ret != 0);
+        return ret;
+    }
+    struct stat st;
+    ret = fstat(fd, &st);
+    if (ret == -1) {
+        ret = errno;
+        assert(ret != 0);
+        close(fd);
+        return ret;
+    }
+    size = st.st_size;
+    if (size > 0) {
+        p = malloc(size);
+    }
+    else {
+        /* Avoid a confusing error */
+        p = malloc(1);
+    }
+    if (p == NULL) {
+        close(fd);
+        return ENOMEM;
+    }
+    ssz = read(fd, p, size);
+    if (ssz != size) {
+        ret = errno;
+        assert(ret != 0);
+        close(fd);
+        return ret;
+    }
+    close(fd);
+    *pp = p;
+    *sizep = size;
+    return 0;
+}
+
+void
+unmap_file(void *p, size_t sz)
+{
+    free(p);
+}