mol2 writer

[Zeerakkhan47]

PR Summary:

Added mol2 writing support

PR Checklist

---

• Includes appropriate unit test(s)
• Appropriate docstring(s) are added/updated
• Code is (approximately) PEP8 compliant
• Issue(s) raised/addressed?

[codecov]

Codecov Report

Attention: Patch coverage is 19.04762% with 17 lines in your changes missing coverage. Please review.

Project coverage is 93.92%. Comparing base (4b1c0ad) to head (a97371e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
gmso/formats/mol2.py	19.04%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #869      +/-   ##
==========================================
- Coverage   94.15%   93.92%   -0.23%     
==========================================
  Files          65       65              
  Lines        6979     7000      +21     
==========================================
+ Hits         6571     6575       +4     
- Misses        408      425      +17     

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[CalCraven]

Okay so @Zeerakkhan47, lookin good. Now we need to check and see which tests should be written. I would copy any test that's in the test_gro.py file that looks similar for reading gro files, i.e. checking basic topologies, molecule or residue reading, and this one for looping through reading and writing and testing that information is saved.