Add support for recursive references

[mrbean-bremen]

• evaluate conditions in sequences lazily to make sure to check the correct dataset
• this also allows recursively defined sequence attributes

Fixes #206. Structured Reports should now be correctly handled.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.35%. Comparing base (e8644e2) to head (49629de).
⚠️ Report is 135 commits behind head on main.

Files with missing lines	Patch %	Lines
dicom_validator/validator/iod_validator.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
- Coverage   89.82%   89.35%   -0.48%     
==========================================
  Files          15       19       +4     
  Lines        1632     1917     +285     
==========================================
+ Hits         1466     1713     +247     
- Misses        166      204      +38     

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