Merge tag 'topic/dma-features-2025-06-23' into alloc-next

Merge tag 'topic/dma-features-2025-06-23' into alloc-next

DMA features for v6.17

- Clarify wording and be consistent in 'coherent' nomenclature.

- Convert the read!() / write!() macros to return a Result.

- Add as_slice() / write() methods in CoherentAllocation.

- Fix doc-comment of dma_handle().

- Expose count() and size() in CoherentAllocation and add the
  corresponding type invariants.

- Implement CoherentAllocation::dma_handle_with_offset().