SceneOptimizer cannot handle dropped cameras before rotation averaging

Although we can handle dropped cameras after DA, we can't before rot averaging:

- Shonan expects a rotation for every single camera frame (which may not exist if we have a subgraph from connected component)
- Alignment cannot handle `None` elements

Maybe to the rotation averaging wrapper we want to add
```python
+ # indices of cameras found inside connected subgraph
+ connected_idxs = set()

for (i1, i2), i2Ri1 in i2Ri1_dict.items():
if i2Ri1 is not None:
+ connected_idxs = connected_idxs.union(set([i1,i2]))

- return [result_values.atRot3(i) for i in range(num_images)]
+ # some camera indices may not have been present in connected component subgraph that is passed in
+ return [result_values.atRot3(i) if i in connected_idxs else None for i in range(num_images)]
```

Start with the rotation averaging wrapper described in the issue, then trace how SceneOptimizer passes its results into Shonan and Alignment. Verify how missing camera indices from a connected-component subgraph are represented, and confirm that disconnected cameras remain None without causing Alignment to fail.

Written by the indexing model from the issue text.