[ty] Benchmark generic tuple class-pattern captures (#29235)
Codex was overfitting its optimizations for tuple match narrowing to
non-generic classes, when generic classes display similar or worse
performance. Update the benchmark to also include the generic-class
case, so we don't fail to optimize that as well.
Add 8- and 16-case variants of the tuple class-pattern capture
benchmark, using writable `T | None` attributes and class instances
specialized with `int`.
The existing non-generic benchmark names and generated inputs are
unchanged.
Related to astral-sh/ty#4676.
