Fix confusing loop start expression in py_c_api.cc

[Copilot]

The dimension-copy loop used num_dims - num_dims as the start value (always 0), which is unnecessarily confusing and prone to type-deduction surprises.

• pyop/py_c_api.cc: Replace auto n = num_dims - num_dims with explicit size_t n = 0; add npy_dims.reserve(num_dims) to avoid unnecessary reallocations.

// Before
std::vector<std::size_t> npy_dims;
for (auto n = num_dims - num_dims; n < num_dims; ++n) {

// After
std::vector<std::size_t> npy_dims;
npy_dims.reserve(num_dims);
for (size_t n = 0; n < num_dims; ++n) {