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/unique_position.proto

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+// Copyright 2012 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Protobuf representation of the UniquePosition class.
+
+// If you change or add any fields in this file, update proto_visitors.h and
+// potentially proto_enum_conversions.{h, cc}.
+
+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;
+
+// A UniquePosition is a string of bytes.
+//
+// Unique positions are unique per-item, since they are guaranteed to end with a
+// fixed-length suffix that is unique per-item.  The position string may not end
+// with a '\0' byte.
+//
+// Prior to the suffix is a series of arbitrary bytes of arbitrary length.
+// Items under the same parent are positioned relative to each other by a
+// lexicographic comparison of their UniquePosition values.
+message UniquePosition {
+  // History:
+  //
+  // Unique positions were first introduced in M28.  This change was rolled out
+  // in such a way that it would try to maintain backwards compatibilty with
+  // clients that understood only the old int64-based positions.
+  //
+  // At first, clients supported only the 'value' field.  This version never
+  // made it to stable.  We later added support for the 'compressed_value'
+  // field, and clients would populate either one or the other.
+  //
+  // In M30, we added the custom_compressed_v1 representation.  This
+  // representation was better than the previous implementations in almost every
+  // way.  However, we could not use it right away, since older clients would
+  // not understand it.  We decided to write both the old-style ('value' or
+  // 'custom_compressed') representation and the 'custom_compressed_v1'
+  // repersentations to every protobuf during the transition period.  Protobufs
+  // written during this transition period would be readable by clients who
+  // understand at least one of the two formats.
+  //
+  // In M33, we dropped support for writing the backwards-compatibility fields.
+  // Protobufs written by this version or later are not be intelligible by
+  // clients with version M29 or older.  Those clients will end up making use of
+  // the old int64 position fallback mechanism.
+
+  // The uncompressed string of bytes representing the position.
+  //
+  // Deprecated.  See history note above.
+  optional bytes value = 1 [deprecated = true];
+
+  // The client may choose to write a compressed position to this field instead
+  // of populating the 'value' above.  If it chooses to use compression, the
+  // 'value' field above must be empty.  The position value will be compressed
+  // with gzip and stored in the compressed_value field.  The position's
+  // uncompressed length must be specified and written to the
+  // uncompressed_length field.
+  //
+  // Deprecated.  See history note above.
+  optional bytes compressed_value = 2 [deprecated = true];
+  optional uint64 uncompressed_length = 3 [deprecated = true];
+
+  // This encoding uses compression scheme designed especially for unique
+  // positions.  It has the property that X < Y precisely when Compressed(X) <
+  // Compressed(Y), which is very useful when the most common operation is to
+  // compare these positions against each other.  Their values may remain
+  // compressed in memory.
+  //
+  // The compression scheme is implemented and documented in
+  // sync/core_impl/base/unique_position.cc.
+  //
+  // As of M30, this is the preferred encoding.  Newer clients may continue to
+  // populate the 'value' and 'compressed_value' fields to ensure backwards
+  // compatibility, but they will always try to read from this field first.
+  optional bytes custom_compressed_v1 = 4;
+}