Add clean dart2wasm web support

[dh0er]

Summary

This adds clean dart2wasm support for the web build while keeping the existing standalone .wasm asset flow.

The package now uses the current universal_ffi release line for web FFI support and avoids package-local Dart code generation for Wasm function signatures. The Wasm asset is built as a standalone module and the asset saver uses an explicit typed lookup for the write_file bridge.

Dependency

This depends on the standalone Wasm function export fix in dh0er/wasm_ffi#2. Without that wasm_ffi change, standalone Wasm exports are surfaced as JSFunction under dart2wasm and cannot be invoked through the existing lookupFunction / asFunction path reliably.

Changes

• Raise the package and example SDK floor to Dart 3.10.8.
• Update universal_ffi to ^1.5.0.
• Build assets/sweph.wasm as standalone Wasm with explicit standalone/web-worker flags.
• Keep -DNO_SWE_GLP for the Wasm build so Swiss Ephemeris does not depend on native library-path behavior.
• Export and use the in-memory write_file bridge for web asset loading.
• Use typed pointer parameters for the web asset saver bridge and call lookup<NativeFunction<...>>(...).asFunction<...>() explicitly.
• Keep the public Sweph.init / web asset loading shape intact.

Validation

• dart pub get
• flutter pub get in example/
• dart analyze
• make wasm
• flutter build web --wasm in example/
• Browser smoke of the Wasm build:
  • renders Sweph Version: 2.10.03
  • renders numeric Moon longitude/latitude
  • renders fixed-star Rohini output
  • renders house ASCMC and house cusp output
  • no current browser error logs for the served build
• flutter build web in example/
• Browser smoke of the JS web build with the same rendered example values
• git diff --check

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Note

Medium Risk
Touches the Wasm build pipeline and FFI boundary for ephemeris file loading on web; behavior was validated manually but depends on external wasm_ffi export fixes.

Overview
Adds dart2wasm-compatible web support by building assets/sweph.wasm as a standalone module (no Emscripten JS shell), with -DNO_SWE_GLP, a stubbed getenv, and an exported write_file bridge for in-memory ephemeris assets.

The Dart side bumps the SDK floor to 3.10.8, upgrades universal_ffi to ^1.5.0, and fixes the web asset saver to use typed lookup<NativeFunction<...>>().asFunction() and Pointer<Uint8> when calling write_file and freeing WASM memory. Examples use textContent on the DOM API; Utf8Pointer.toDartString is a small refactor only.

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