fix: slow rendering

[erdostw]

Speed up rendering process with a smarter use of tree-seq on the model tree.

See for details: #81

[codecov-commenter]

Codecov Report

Merging #82 (6e46c87) into master (e8755c4) will decrease coverage by 0.20%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
- Coverage   92.32%   92.11%   -0.21%     
==========================================
  Files          24       24              
  Lines        1824     1827       +3     
  Branches      113      117       +4     
==========================================
- Hits         1684     1683       -1     
  Misses         27       27              
- Partials      113      117       +4     

Impacted Files	Coverage Δ
src/stencil/api.clj	93.61% <ø> (ø)
src/stencil/model/numbering.clj	94.11% <ø> (ø)
src/stencil/process.clj	74.41% <ø> (ø)
src/stencil/model.clj	95.09% <85.71%> (-2.41%)	⬇️

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