v1.0.0 of exath_engine

Flutter plugin for the exath-engine: a complex-native math evaluator with computer algebra (diff, factor, solve, integral, linear algebra), prebuilt for every platform. Changelog excerpt: - First release of exath_engine: a Flutter plugin for the exath-engine, a complex-native math evaluator with a computer-algebra core. Prebuilt native libraries are bundled for Android, iOS, macOS, Windows, and Linux, and the WASM module is bundled for web. Call await ensureInitialized()once at startup (loads the WASM module on web, no-op elsewhere).