Grid mapping rules

[forman]

Added a few more grid mapping rules

Checklist (strike out non-applicable):

• Changes documented in CHANGES.md
• Related issue exists and is referred to in the PR description and CHANGES.md
• Added docstrings and API docs for any new/modified user-facing classes and functions
• Changes/features documented in docs/*
• Unit-tests adapted/added for changes/features
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

Attention: Patch coverage is 97.15909% with 5 lines in your changes missing coverage. Please review.

Project coverage is 93.64%. Comparing base (e232629) to head (7703bed).
Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
xrlint/cli/main.py	84.61%	1 Missing and 1 partial ⚠️
xrlint/config.py	91.66%	1 Missing and 1 partial ⚠️
xrlint/plugins/core/rules/var_units_attr.py	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   92.92%   93.64%   +0.72%     
==========================================
  Files          40       46       +6     
  Lines        1272     1385     +113     
  Branches      158      180      +22     
==========================================
+ Hits         1182     1297     +115     
+ Misses         55       53       -2     
  Partials       35       35              

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