chore: extract unifont

[florian-lefebvre]

Working on unifont this week, I found that having createUnifont() in the main entrypoint was a bit confusing, as it made less clear what was re-exported from here. In this PR, I extracted it to its distinct file and keep index.ts as a barrel export. Will help for #288 types exports

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.91%. Comparing base (92ceb7a) to head (22edf03).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #292   +/-   ##
=======================================
  Coverage   98.91%   98.91%           
=======================================
  Files          11       11           
  Lines         460      460           
  Branches      113      113           
=======================================
  Hits          455      455           
  Misses          5        5           

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[danielroe]

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