Add a place holder binary for private memory server.

So that we can go through the transparent release process earlier.

ACKNOWLEDGE_FAILING_COPYBARA_IMPORT=The failure is not caused my this
change. cl/726948285 can be used for fixing tests while importing.

BUG: 396479186
Change-Id: Ib034a75a34bb5252deca71ac5bf5acdecd9d4a5d

oak_private_memory/BUILD

@@ -0,0 +1,27 @@
+#
+# Copyright 2025 The Project Oak Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+load("@rules_rust//rust:defs.bzl", "rust_binary")
+
+package(
+    default_visibility = ["//:internal"],
+    licenses = ["notice"],
+)
+
+rust_binary(
+    name = "private_memory_server",
+    srcs = ["src/main.rs"],
+)

oak_private_memory/README.md

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+# Private memory
+
+This directory contains the source code of private memory.

oak_private_memory/src/main.rs

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+//
+// Copyright 2025 The Project Oak Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+fn main() {
+    println!("This is placeholder binary for private memory!");
+}