Allow unreduced/reduced to work when check_vma=False.
**What does this mean?**
When check_vma=False, shard_map's type system won't track unreduced, reduced, invarying and varying anymore.
For example: The only way from unreduced -> varying when check_vma=True is via a reduce_scatter but when check_vma=False, this is just a bitcast. Concretely:
Assume you have 2 devices:
**With check_vma=True:**
```
unreduced --RS--> varying
D0 D1
[0 1 | 2 3] ---reduce-scatter---> [2 | 4]
```
Shape changes:
* Global shape: `(2,) -> (2,)`
* Device local shape: `(2,) -> (1,)`
**With check_vma=False:**
```
unreduced ---bitcast---> varying
D0 D1
[0 1 | 2 3] ---> [0 1 | 2 3]
```
Shape changes:
* Global shape: `(2,) -> (4,)`
* Device local shape: `(2,) -> (2,)`
The bitcast is similar for replicated <-> unreduced as sharded <-> unreduced.
PiperOrigin-RevId: 862901355
