[thrust] Use CCCL Runtime in CUDA extrema tests

Part of #2800.

Use CCCL Runtime APIs in a small batch of Thrust CUDA extrema tests.

Candidate files:

- `thrust/testing/cuda/max_element.cu`
- `thrust/testing/cuda/min_element.cu`
- `thrust/testing/cuda/minmax_element.cu`

Group by the extrema test family. Within selected files, apply all approved Runtime substitutions that naturally fit. Avoid changing Thrust behavior that is directly under test.