Widen specialized int fast paths to full int64 range

This work widens the interpreter’s specialized int fast paths (tier-2 / uop execution) from the compact-only range to the full int64_t range.

It also fixes follow-up correctness issues in the widened specialized paths for non-compact exact PyLongObjects and on 15-bit builds.

Scope:

• widen specialized integer add/subtract/multiply fast paths to operate across the full int64_t range
• accept exact int operands that fit in int64_t, including non-compact PyLongObjects
• keep specialized in-place mutation compact-only and fall back safely for non-compact inputs
• handle widened integer compare without compact-only assumptions
• construct widened arithmetic results with PyLong_FromInt64() so 15-bit builds do not narrow through stwodigits
• add regression coverage for widened operations, non-compact exact ints, boundary cases, and overflow fallback
• add benchmark scripts for measuring widened specialized integer fast-path performance

Linked PRs

• gh-150425

まず、インタープリターの tier-2/uop における整数の加算、減算、乗算、比較用の特殊化された高速パスを、PyLongObject オペランドの処理も含めて見つけます。拡張された演算向けに追加されたリグレッションカバレッジとベンチマークスクリプトを確認し、その後、int64_t の全範囲の境界、非コンパクトな Exact Int、オーバーフロー時のフォールバック、インプレースミューテーションの挙動、15-bit ビルドを検証します。