fix: report dataset provider errors as failing tests (#1749)

Errors raised while resolving a test's dataset (missing named dataset,
throwing dataset closure) previously crashed the whole run. Now the data
provider catches them, wraps them in a DatasetProviderError, and the test
method rethrows the original throwable so the affected test fails cleanly
with a non-zero exit code while other tests keep running.

tests/.tests/DatasetClosureThrows.php

@@ -0,0 +1,9 @@
+<?php
+
+dataset('throws', function () {
+    throw new RuntimeException('boom from dataset');
+});
+
+it('x', function ($a) {
+    expect($a)->toBeTrue();
+})->with('throws');