render abstract method
template rendered against context, or a refusal explaining why not.
context is any JSON-shaped model: strings, numbers, booleans, lists,
and maps. Mustache truthiness decides sections, so an empty list takes
the {{^…}} branch. name names the template in diagnostics.
The result is a value, never a throw: a template that does not compile
comes back as Err, ready to return as a DmxRefusal.
Implementation
Future<Result<String, DmxRefusal>> render(
String template,
Map<String, Object?> context, {
String name = 'template',
});