`Where` (and maybe other symbols) use a default initialization for their `SizeInfo` when dynamic, preventing their state from being serialized

```python
>>> model = dwave.optimization.Model()
>>> where = dwave.optimization.where(model.binary(), model.set(100), model.set(100))
>>> where.state_size()
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
Cell In[5], line 1
----> 1 where.state_size()

File ~/dwave-optimization/dwave/optimization/_model.pyx:1867, in dwave.optimization._model.ArraySymbol.state_size()
1865 # This shouldn't happen, but just in case...
1866 if not sizeinfo.max.has_value():
-> 1867 raise RuntimeError("size is unbounded")
1868
1869 return sizeinfo.max.value() * self.array_ptr.itemsize()

RuntimeError: size is unbounded
```