fix(fontless): emitFile during transform

[hi-ogawa]

problem

When using "shared plugin mode" during build https://vite.dev/guide/api-environment-plugins.html#shared-plugins-during-build, plugin's assetContext.renderedFontURLs state is shared between all environment builds and it causes emitFile during generateBundle to doubly/triply output font assets on unrelated environments. For example, this is the case on @vitejs/plugin-rsc based app and it currently causes css and font processed on rsc environment to cause other environments to also write font files.

solution

This PR moves emitFile from generateBundle to assetContext.callback, which is called only when transformCss found a relevant assets and this avoids generating fonts in an unrelated environment.

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🔨 Latest commit	03610f9
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npm i https://pkg.pr.new/fontaine@653

npm i https://pkg.pr.new/fontless@653

commit: 03610f9

[codecov]

Codecov Report

❌ Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.90%. Comparing base (d66809d) to head (03610f9).

Files with missing lines	Patch %	Lines
packages/fontless/src/vite.ts	0.00%	29 Missing ⚠️
packages/fontless/src/assets.ts	0.00%	4 Missing ⚠️
packages/fontless/src/resolve.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #653      +/-   ##
==========================================
- Coverage   53.40%   52.90%   -0.50%     
==========================================
  Files          11       11              
  Lines         734      739       +5     
  Branches       93       93              
==========================================
- Hits          392      391       -1     
- Misses        342      348       +6     

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