Optimize eltype handling

[ytdHuang]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.52%. Comparing base (0022be9) to head (169eafb).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/HierarchicalEOM_CUDAExt.jl	0.00%	1 Missing ⚠️
src/HeomBase.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #111      +/-   ##
==========================================
- Coverage   92.11%   89.52%   -2.59%     
==========================================
  Files          20       20              
  Lines        1484     1461      -23     
==========================================
- Hits         1367     1308      -59     
- Misses        117      153      +36     

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