NaN Values in Gradients Cause Calculation Abortion Using Mixed Precision with GPU Offload

**Describe the bug**
When running a periodic calculation with 9 twists, 724 electrons, and 44 atoms using the mixed precision version of QMCPACK with GPU offload, the calculation was aborted with the following error:
```
NaNguard::checkOneParticleGradients error message: TWF::calcRatioGrad at particle 687
grads[0] = (-nan,0.0418255)
grads[1] = (-nan,-0.0806002)
grads[2] = (-nan,0.0412396)
Unexpected exception thrown in threaded section
Fatal Error. Aborting at Unhandled Exception
This issue appears to be related to NaN values in the gradients of the wave function for a specific particle.
```
The same calculation with full precision ran smoothly without any problems.

**To Reproduce**
Input and output files below:
[dmc_2x2_single_prec-test.zip](https://github.com/user-attachments/files/15506869/dmc_2x2_single_prec-test.zip)

**Expected behavior**
The calculation should complete successfully without encountering NaN values in the wave function gradients, resulting in accurate and stable output data.

**System:**
System name: Perlmutter
Modules loaded:
module use /global/common/software/nersc/n9/llvm/modules
module load craype cray-mpich
module load llvm/17.0.6-gpu
Other systems where this is reproducible: Not tested on other systems.

**Additional context**
The calculation was performed using the complex version of QMCPACK with NVIDIA GPU and OpenMP offload.
No other context or error messages where in the output files.