Improve stability of heat diffusion solver

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.92308% with 54 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
src/ext/AMDGPU/2D.jl	0.00%	12 Missing :warning:
src/ext/AMDGPU/3D.jl	0.00%	12 Missing :warning:
src/ext/CUDA/2D.jl	0.00%	12 Missing :warning:
src/ext/CUDA/3D.jl	0.00%	12 Missing :warning:
src/thermal_diffusion/DiffusionPT_coefficients.jl	66.66%	4 Missing :warning:
src/thermal_diffusion/DiffusionPT_kernels.jl	50.00%	2 Missing :warning:

Additional details and impacted files

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