refactor(editor): use model coord system in worker renderer

[doodlewind]

In original PoC, the canvas is rendered using DOM coords from getBoundingClientRect directly, which is not scalable. This PR switches to using model coords when rendering offscreen text sections.

[graphite-app]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.02%. Comparing base (db1fcf4) to head (e359e24).
Report is 5 commits behind head on canary.

Additional details and impacted files

@@            Coverage Diff             @@
##           canary    #9969      +/-   ##
==========================================
- Coverage   53.03%   53.02%   -0.01%     
==========================================
  Files        2257     2257              
  Lines      103235   103235              
  Branches    17159    17156       -3     
==========================================
- Hits        54750    54742       -8     
- Misses      47104    47111       +7     
- Partials     1381     1382       +1     

Flag	Coverage Δ
server-test	76.44% <ø> (-0.02%)	⬇️
unittest	31.84% <100.00%> (ø)

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