Fix GPU problems in pulse_MG.cpp

[chongchonghe]

Description

I discovered some GPU-related issues in radhydro_pulse_MG.cpp and fixed it. In the previous PR, I turned if off for 3D problems because it is too expensive. As a result, it didn't get to compile and run on nvcc or ROCm. I fixed some first-capture and undefined on device issues and turned this test (and radhydro_pulse_MG_int.cpp) on. I set max_timesteps=10 in these tests in order to let them finish fast. We are not comparing with exact solutions any way (because there isn't one), so it's okay to run only a small number of time steps and show that the architecture is working. The accuracy of the multigroup implementation is tested by hand, and I will include it in a planned nightly unit test.

Checklist

Before this pull request can be reviewed, all of these tasks should be completed. Denote completed tasks with an x inside the square brackets [ ] in the Markdown source below:

• I have added a description (see above).
• I have added a link to any related issues see (see above).
• I have read the Contributing Guide.
• I have added tests for any new physics that this PR adds to the code.
• I have tested this PR on my local computer and all tests pass.
• I have manually triggered the GPU tests with the magic comment /azp run.
• I have requested a reviewer for this PR.

[chongchonghe]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 5 pipeline(s).

[chongchonghe]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 5 pipeline(s).