Make nested models share coords with parents

[lucianopaz]

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Closes #5343

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• what are the (breaking) changes that this PR makes?
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[codecov]

Codecov Report

Merging #5344 (ec18b5d) into main (b29124b) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5344      +/-   ##
==========================================
+ Coverage   80.19%   80.21%   +0.02%     
==========================================
  Files          89       89              
  Lines       14845    14848       +3     
==========================================
+ Hits        11905    11911       +6     
+ Misses       2940     2937       -3     

Impacted Files	Coverage Δ
pymc/model.py	84.22% <100.00%> (+0.06%)	⬆️
pymc/parallel_sampling.py	87.70% <0.00%> (+0.99%)	⬆️