make extract_atom, extract_global, and gather typestable

[Joroks]

I managed to make extract_atom, extract_global, and gather typestable through constant propagation. These changes are unavoidably breaking, but I strongly believe that this is for the better.

I still have to update documentation and a few checks I probably also need to check that I haven't messed up anywhere but everything seems to be working at least.

I think we could also have a similar issue with cache invalidation as we have with BIGINT etc. But I'm not familiar enough with the internals of julia to know for sure.

I'd like to know your opinion on this @vchuravy
(P.s. I'm sorry for the large and messy PR)

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Codecov Report

Attention: Patch coverage is 91.60305% with 11 lines in your changes missing coverage. Please review.

Project coverage is 72.81%. Comparing base (b60ac24) to head (c3b1ff1).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/LAMMPS.jl	91.60%	11 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
- Coverage   73.12%   72.81%   -0.31%     
==========================================
  Files           2        2              
  Lines         480      493      +13     
==========================================
+ Hits          351      359       +8     
- Misses        129      134       +5     

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[Joroks]

I had to use Symbols instead of Strings as the constant propagation didn't work otherwise. I decided to make this a universal change.