fix(solid_generator): cross-instance @SolidState in mixed-file pure consumers (dev.10)

[nank1ro]

Problem

Whole-file pure-consumer lowering (lowerPureConsumers) only runs when every class in a file is annotation-free. In a mixed file — a no-annotation presentation widget/class co-located with the annotated class it consumes — _resultForClass passed the consumer through verbatim. So a cross-instance @SolidState write through a plain constructor/instance field:

class Counter { @SolidState() int count = 0; }

class CounterView extends StatelessWidget {
  const CounterView({required this.counter});
  final Counter counter;                                   // plain field
  Widget build(_) => GestureDetector(
    onTap: () => counter.count = counter.count + 1,        // NOT lowered
    child: Text('${counter.count}'),                       // NOT lowered / not reactive
  );
}

stayed un-lowered → counter.count = … hit assignment_to_final on the generated final Signal, and the read stayed non-reactive (no SignalBuilder).

Fix

New per-class lowerPureConsumerClass (mirrors the two whole-file collectors: build → rewriteBuildMethod for .value + wrap; other ctors/methods → collectValueEdits; applied via applyEditsToRange(slice, edits, decl.offset)). _resultForClass calls it for hasNoAnnotations classes instead of a verbatim passthrough, returning {'SignalBuilder'} on wrap so flutter_solidart is imported. The pure consumer is not lifted and gains no Disposable — it owns no reactive member.

Tests

• New goldens mixed_file_pure_consumer_widget (StatelessWidget: write+read lowered, wrapped, imported) and mixed_file_pure_consumer_plain_class (plain class: read+write lowered, no wrap, no Disposable).
• Full suite 372/372 (incl. idempotency), dart analyze lib clean.

Reviewed by 2 adversarial reviewers (0 findings). Bumps solid_generator to 3.0.0-dev.10.