Add initial support for handling functional groups

[mrbean-bremen]

• add functional group macro info to iod info
• add special handling for functional groups
• still missing: handle macros that are not allowed in either shared or per-frame groups handle duplicate tags in both groups

This is ongoing work, but I'll probably merge an initial version first, and handle other problems first before going back to this.

[codecov-commenter]

Codecov Report

Merging #31 (e4de9a5) into main (4a3ac43) will increase coverage by 0.07%. The diff coverage is 90.22%.

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
+ Coverage   87.55%   87.62%   +0.07%     
==========================================
  Files          14       14              
  Lines        1374     1471      +97     
==========================================
+ Hits         1203     1289      +86     
- Misses        171      182      +11     

Files Changed	Coverage Δ
dicom_validator/validator/iod_validator.py	91.78% <88.46%> (-1.70%)	:arrow_down:
dicom_validator/spec_reader/part3_reader.py	96.20% <95.45%> (+0.39%)	:arrow_up:

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