Pydantic 2.2.0 fixes

[dapper91]

• decimal type support added. fixes Decimal fields raise ModelError with pydantic version 2.2 #93.
• unparameterized root models serializer generation bug fixed. Affected by Don't always require typing.Generic as a base for partially parametrized models pydantic/pydantic#7119 change.

[codecov-commenter]

Codecov Report

Merging #95 (ea3eb97) into dev (a6d40e6) will decrease coverage by 1.03%.
Report is 42 commits behind head on dev.
The diff coverage is 93.28%.

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@@            Coverage Diff             @@
##              dev      #95      +/-   ##
==========================================
- Coverage   93.11%   92.09%   -1.03%     
==========================================
  Files          23       23              
  Lines        1089     1239     +150     
==========================================
+ Hits         1014     1141     +127     
- Misses         75       98      +23     

Flag	Coverage Δ
unittests	92.09% <93.28%> (-1.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
pydantic_xml/element/native/lxml.py	0.00% <ø> (ø)
...ydantic_xml/serializers/factories/typed_mapping.py	73.91% <73.91%> (ø)
pydantic_xml/serializers/factories/tagged_union.py	84.84% <84.84%> (ø)
pydantic_xml/serializers/factories/union.py	87.95% <87.17%> (+0.14%)	⬆️
pydantic_xml/serializers/factories/mapping.py	88.75% <89.33%> (-1.88%)	⬇️
...ydantic_xml/serializers/factories/heterogeneous.py	89.58% <90.90%> (-1.49%)	⬇️
pydantic_xml/serializers/factories/homogeneous.py	92.00% <91.66%> (+0.62%)	⬆️
pydantic_xml/serializers/factories/primitive.py	95.69% <95.45%> (+1.66%)	⬆️
pydantic_xml/serializers/factories/model.py	95.62% <96.04%> (+0.34%)	⬆️
pydantic_xml/serializers/serializer.py	95.86% <96.37%> (-1.62%)	⬇️
... and 8 more