Added simple rounding error solution

[pbuslaev]

Description

This is a proposed solution for #1166 on the GROMACS writer side.

If this approach is approved I can add tests/parameters

Checklist

• [ ] Add tests
• [ ] Lint
• [ ] Update docstrings

[codecov[bot]]

Codecov Report

:x: Patch coverage is 35.29412% with 11 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 93.22%. Comparing base (6426579) to head (dd48e2e). :warning: Report is 198 commits behind head on main.

Files with missing lines	Patch %	Lines
...enff/interchange/interop/gromacs/export/_export.py	31.25%	11 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1167      +/-   ##
==========================================
- Coverage   93.38%   93.22%   -0.17%     
==========================================
  Files          70       70              
  Lines        6036     6050      +14     
==========================================
+ Hits         5637     5640       +3     
- Misses        399      410      +11     

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[mattwthompson]

@pbuslaev what do you think about trying to fix this problem earlier by "fixing" charges during Interchange.from_openmm?