v0.19.0

This release lets Dart consume JavaScript async iterables returned by callbacks,
preserves custom const collection defaults, and supports rebuilding generated
npm packages on Linux.

🔁 Consume async iterables from Dart callbacks

A callback declared with a Dart Stream result now accepts a JavaScript
AsyncIterable, including an async generator:

@NAPI()
Future<List<int>> read(Stream<int> Function(int) source) => source(3).toList();

await read(async function* (start) {
  yield start;
  yield start + 1;
}); // [3, 4]

Dart pulls one item at a time and validates each yielded value. Pausing stops
further pulls; cancelling or failing conversion calls the iterator's optional
return() once. Original JavaScript iteration errors retain their identity.

Resource payloads stay retained through iteration. Closing a resource requests
cancellation and waits for accepted iterator work; it cannot force an unresolved
JavaScript Promise to settle. Both native and Wasm use the same mapping.

Stream callback behavior

📦 Keep custom const collection defaults

Optional parameters can now use custom const List and Map implementations
with scalar or structural data elements. Omitting a parameter or supplying
undefined preserves the original Dart constant, including nested collections.
Explicit JavaScript inputs keep the ordinary declared collection conversions.

The constant needs an accessible constructor or public const binding. Resources
stored in its fields retain their normal operation leases without evaluating
collection getters or iterators. Reference, value-class and opaque element types
remain unsupported because computed elements need not appear in stored fields.

Argument defaults and limits

🐧 Rebuild generated npm packages on Linux

Build and assembly calls can now replace their own managed output on supported
64-bit Linux ext-family filesystems and tmpfs. Replacement uses an atomic
directory exchange and preserves retained author files, permissions, ownership,
ACLs, extended attributes and timestamps for unchanged files. Linux requires
statx and extended attribute support; legacy or unsupported output remains
unchanged.

This extends package rebuilding. Native .node addons still support macOS
arm64.

Managed rebuild rules

Other improvements and fixes

• Managed rebuilds can replace explicitly supplied read-only documentation assets
  and preserve read-only package.json permissions on Linux.

Regenerate bindings to use the new conversions. Both build targets still require
Dart 3.13.5; native packages use bridge ABI 15.