Prepare release

[simolus3]

This prepares a patch release of the Dart SDK. Relevant changes are:

• Update package:sqlite3 and package:sqlite_async (Update sqlite packages #314 and Update package:sqlite3 for wasm build #313).
• Support the unified format for HTTP errors from the sync service (Use new error response format to parse errors #309).
• Support BSON sync lines with the Rust client (Rust client: Request sync lines as BSON #312).
• Improving disconnect() while we're currently establishing a connection (Request cancellation #315)