sqlite: remove the null prototype from result rows

Current behavior

Rows returned by get(), all() and iterate() are created with a null prototype. The V8 API that does this produces dictionary-mode objects, and V8 will not cache a prototype transition on a dictionary map, so every row also gets its own freshly allocated hidden class. Rows from the same statement therefore share no shape: they are slow to build, and every property access on them in user code is megamorphic.

Proposal

Drop the null prototype and build rows with v8::DictionaryTemplate, cached per statement. Rows become ordinary objects, and every row of a statement shares one hidden class.

Pros

• all() is 10–37% faster depending on the query; reading the rows afterwards is far cheaper still.
• Consistent with run(), which already returns an ordinary object, and with better-sqlite3.

Cons

• Semver-major.
• Rows can no longer be indexed by untrusted keys without Object.hasOwn() — row.toString and row.constructor start resolving through Object.prototype.
• User code comparing rows against { __proto__: null, ... } breaks.

Prototype pollution is not a concern either way: rows are built by defining own properties directly, so a __proto__ column is an own property and never reaches Object.prototype.

I have benchmarks and a working implementation if there is interest.

まず、get()、all()、iterate() の実装と、既存の run() の結果処理を探し、次に V8 API と v8::DictionaryTemplate がどのように使用されているかを確認します。issue で言及されている提案ベンチマークと動作する実装を確認します。通常のオブジェクトの挙動、共有される行の形状、パフォーマンス、semver-major に関する互換性上の懸念を評価すれば完了です。