Fix optimizer checkpoint state round-trip

[koriyoshi2041]

Fixes #9.

The optimizer wrapper now saves its own perturbation state, wrapper attributes, scheduler state, and the wrapped base optimizer in a versioned checkpoint. Loading keeps compatibility with legacy base-only checkpoints and rebinds the shared parameter groups.

The scheduler follow-up adds explicit phase round-tripping for INFTY schedulers and for the wrapped PyTorch scheduler used by ProportionScheduler. The resume regression advances both continuous and restored paths and compares the next scheduled value and LookSAM parameter update.

Validation:

• uv run --frozen --with pytest --with pyyaml pytest -q — 33 passed
• uv run --frozen --with pytest pytest tests/optim/test_geometry_reshaping.py -q — 4 passed
• git diff --check

Known boundary: runtime closures are deliberately reattached with set_closure() rather than serialized. The separate LookSAM old_g / old_grad mismatch is not part of this checkpoint fix.

[koriyoshi2041]

Small follow-up after rechecking the current head (ebf43ab): the PR remains cleanly mergeable. The focused optimizer suite passed 10/10 when I submitted it, including versioned and legacy checkpoint loading plus next-step numerical equivalence after restore. Happy to add narrower coverage if there is a checkpoint-compatibility case you want exercised before review.