Add PNNS SerializedProcessedDatabase (#9)

Author: fboemer

apple/swift_homomorphic_encryption/pnns/v1/pnns_processed_database.proto

@@ -0,0 +1,31 @@
+// Copyright 2024 Apple Inc. and the Swift Homomorphic Encryption project 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.
+
+syntax = "proto3";
+package apple.swift_homomorphic_encryption.pnns.v1;
+
+import "apple/swift_homomorphic_encryption/pnns/v1/pnns.proto";
+import "apple/swift_homomorphic_encryption/pnns/v1/pnns_server_config.proto";
+
+// Serialized pre-processed nearest neighbors database.
+message SerializedProcessedDatabase {
+  // Pre-computed values for the nearest neighbors computation, one per plaintext CRT modulus.
+  repeated SerializedPlaintextMatrix plaintext_matrices = 1;
+  // Unique identifier for each entry in the database.
+  repeated uint64 entry_ids = 2;
+  // Metadata for each entry in the database.
+  repeated bytes entry_metadatas = 3;
+  // Configuration used to create the database.
+  ServerConfig server_config = 4;
+}