build method
Runs the GraphLink code generator for the current BuildStep.
Reads all .graphql / .graphqls files under lib/, parses the merged
schema, and writes generated Dart files to outputDir.
Implementation
@override
Future<void> build(BuildStep buildStep) async {
final now = DateTime.now();
await initAssets(buildStep);
// Merge any unknown string options into type mappings (custom scalars).
options.config.entries
.where((e) => e.value is String && !_knownOptions.contains(e.key))
.forEach((e) => typeMappings[e.key] = e.value as String);
final config = _buildConfig();
final grammar = createGrammar(config);
final schema = await readSchema(buildStep);
grammar.parse(schema);
await generateDartClientClasses(grammar, config, now);
}