build: use pydantic-compat library

[tlambert03]

I pulled out most of the pydantic cross-compatibility stuff that I added in #122 (along with stuff I did for ome-types and psygnal), and make a new library: https://github.com/tlambert03/pydantic-compat

this PR uses it and pulls out most of the patch logic here

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.10% 🎉

Comparison is base (91fb059) 98.28% compared to head (fb478df) 98.39%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
+ Coverage   98.28%   98.39%   +0.10%     
==========================================
  Files          15       15              
  Lines         877      811      -66     
==========================================
- Hits          862      798      -64     
+ Misses         15       13       -2     

Files Changed	Coverage Δ
src/useq/__init__.py	100.00% <100.00%> (ø)
src/useq/_base_model.py	100.00% <100.00%> (ø)
src/useq/_grid.py	100.00% <100.00%> (ø)
src/useq/_hardware_autofocus.py	100.00% <100.00%> (ø)
src/useq/_iter_sequence.py	100.00% <100.00%> (ø)
src/useq/_mda_event.py	87.50% <100.00%> (+0.26%)	⬆️
src/useq/_mda_sequence.py	98.65% <100.00%> (-0.01%)	⬇️
src/useq/_pydantic_compat.py	100.00% <100.00%> (+3.70%)	⬆️
src/useq/_utils.py	98.38% <100.00%> (-0.03%)	⬇️
src/useq/_z.py	98.43% <100.00%> (ø)

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