[FEA]: Investigate Load Balancing in Segmented Scan

### Is this a duplicate?

- [x] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this request and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Area

CUB

### Is your feature request related to a problem? Please describe.

As of today, we assign fixed thread granularity to each segment, which leads to load imbalance issues. https://github.com/NVIDIA/cccl/issues/7741 highlights importance of load balaning in practical applications of segmented scan.

### Describe the solution you'd like

Apply load balancing mechanisms described in https://github.com/NVIDIA/cccl/issues/7741 highlights in segmented scan.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_