Port Brave Sync server to Rust

Use SQLite for persistence and generate Rust protobuf bindings at build time.

Add Docker image support for containerized deployment.

Co-Authored-By: codex <[email protected]>

schema/protobuf/sync_pb/experiment_status.proto

@@ -0,0 +1,45 @@
+// Copyright 2014 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// NOTE: This API is not used in Chromium anymore, but the server still needs to
+// support it for the benefit of older clients (Chrome versions up to and
+// including M80 rely on it, see crbug.com/1009361).
+
+syntax = "proto2";
+
+option go_package = "./sync_pb";
+
+option java_multiple_files = true;
+option java_package = "org.chromium.components.sync.protocol";
+
+option optimize_for = LITE_RUNTIME;
+
+package sync_pb;
+
+import "experiments_specifics.proto";
+
+// This request allows an unauthenticated client to check the status of the
+// experiments which do not require user authentication.  The status of an
+// experiment for a specific client can be determined based on the user agent
+// string and/or the client id sent in the HTTPS POST request.
+message ExperimentStatusRequest {
+  // Enumerates the experiments for which the status should be returned.  An
+  // experiment name must be the same as one of the field names specified in
+  // ExperimentsSpecifics.  See sync/protocol/experiments_specifics.proto.
+  repeated string experiment_name = 1;
+}
+
+// Response to an experiment status request.
+message ExperimentStatusResponse {
+  // Minimal time to wait before issuing another request.
+  optional int32 poll_interval_seconds = 1 [default = 3600];
+
+  // The experiments that the client has asked for, with each experiment
+  // containing exactly one experiment flag.  The client can inspect the
+  // embedded flag to obtain the experiment status.  Note that the number of
+  // experiments should be less than or equal to the number of experiment_name
+  // sent in the request since it is possible that there is no experiment
+  // matching an experiment_name.
+  repeated ExperimentsSpecifics experiment = 2;
+}