[FEA]: Intrusive Decoupled Look-Back

### 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.

Decoupled look-back is the foundation of most CUB algorithms. The decoupled look-back's tile state consists of a message and a flag. Since the message part is considered opaque, we have to double its size to store a few flag bits. When the message type is U32, we double it and use the U64 tile state. When the message type is U64, we use `ulonglong2`. When the message size exceeds 64 bits, we can no longer combine the message and the flag into a single architectural word and have to allocate flags as a standalone memory, which forces us to use memory fences, significantly deteriorating performance.

There are often unused bits in the user types. For instance, if the user type is a pair of U8 and U64, there are padding bits that we could reuse for storing the flag. Alternatively, when dealing with 64-bit integers, the high bits are frequently unused. This is the case when these integers represent sizes or offsets.

### Describe the solution you'd like

We should implement an intrusive version of decoupled look-back. The API would allow us to store the decoupled look-back flag in the message. CUB needs this API to optimize algorithms like partition and select for 64-bit problem sizes, but it would also be helpful on the user side.

### Tasks
- [ ] Design intrusive decoupled look-back API
- [ ] Use intrusive decoupled look-back API in three-way partition
- [ ] Expose intrusive decoupled look-back as public API

### Describe alternatives you've considered

_No response_

### Additional context

_No response_