Generalize spectrum calculation and optimize runtests

[ytdHuang]

Closes #37

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (1bb29d0) 92.83% compared to head (70562d6) 91.39%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
- Coverage   92.83%   91.39%   -1.44%     
==========================================
  Files          20       20              
  Lines        1493     1511      +18     
==========================================
- Hits         1386     1381       -5     
- Misses        107      130      +23     

Files	Coverage Δ
src/HierarchicalEOM.jl	100.00% <ø> (ø)
src/precompile.jl	100.00% <100.00%> (ø)
src/Spectrum.jl	91.05% <95.12%> (-8.95%)	⬇️

... and 8 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.