Fix async sync error conversion

[Flob365]

Summary

• make the promise API sync() await the native promise so rejected errors go through convertError
• add a regression test for Database.sync() after close() returning the same TypeError as other promise API methods

Fixes #147.

Verification

• npm exec tsc
• git diff --check
• npm test partially: SQLite provider tests passed; libSQL/native tests could not run in this environment because cargo is not installed, so the native libsql-darwin-arm64 binding could not be built.