Update the assign function inside both CPU and GPU class

[sjsprecious]

This PR introduces a new Copy function in both the CPU and GPU matrix class.

In the CPU matrix class, it simply calls the assign function.

In the GPU matrix class, it only copies the device data.

All the 42 tests all passed on Derecho's A100 GPU by using nvhpc/23.7.

fix #471

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 92.95%. Comparing base (8aa1caf) to head (0f9f94a).

Files	Patch %	Lines
include/micm/solver/rosenbrock.inl	71.42%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #495 +/- ## ========================================== + Coverage 92.94% 92.95% +0.01% ========================================== Files 42 42 Lines 3258 3266 +8 ========================================== + Hits 3028 3036 +8 Misses 230 230 ```

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