Sample Failures on macos - multidevice and callbackcpp

The `multidevice` and `callbackcpp` tests are failing on macos.

Specifically:

* `multidevice` (and `multidevicecpp`) is failing due to an error returned by `clCreateSubBuffer`, see: https://github.com/bashbaug/OpenCL-SDK/actions/runs/17273274320/job/49023554409
* `callbackcpp` is segfaulting for release builds only, see: https://github.com/bashbaug/OpenCL-SDK/actions/runs/17270551550/job/49013861064

We should debug these failures to check if they are PoCL issues or sample issues, and re-enable the tests when they are passing.

Start with the linked GitHub Actions logs for the macOS multidevice, multidevicecpp, and callbackcpp failures. Reproduce the clCreateSubBuffer error and the release-only callbackcpp segfault, then determine whether each is a PoCL or sample issue. Done means the failures are resolved and the tests are re-enabled when passing.

Written by the indexing model from the issue text.