Platform instance is cached at class load, blocking desktop and web

[developerjamiu]

// lib/src/smart_text_flutter.dart:9
static final _smartTextFlutter = SmartTextFlutterPlatform.instance;

This captures the platform instance once, at class load. Any later assignment to SmartTextFlutterPlatform.instance has no effect.

That defeats the override point plugin_platform_interface exists to provide, and it is why the plugin is awkward to fake in tests.

It also blocks desktop and web support. Flutter registers Dart-only platform implementations by calling a static registerWith() that assigns the instance, exactly as package_info_plus does:

static void registerWith() {
  PackageInfoPlatform.instance = PackageInfoPlusLinuxPlugin();
}

If _smartTextFlutter has already captured the default, that assignment does nothing and the Windows, Linux or web implementation is silently ignored.

Fix: read SmartTextFlutterPlatform.instance per call rather than caching it.

Found during the v0.4.0 codebase audit.