fix(fontless): add immutable cache-control during dev to prevent font flashes on ssr frameworks

[hi-ogawa]

problem

I've been testing out in some ssr frameworks (cf. #651) and I noticed in some frameworks, the same css is loaded on ssr and on client, which causes texts to briefly flashes by going through "with font -> without font -> with font" phases (note this happens even if font is preloaded during dev).

solution

The issue can be prevented by adding long cache to font asset, which allows browser to not request the 2nd font request.

how to test

I manually tested on sveltekit example https://github.com/hi-ogawa/reproductions/tree/main/fontless-sveltekit with the preview release.

[netlify]

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[pkg-pr-new]

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npm i https://pkg.pr.new/fontaine@665

npm i https://pkg.pr.new/fontless@665

commit: 6340fe0

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 53.40%. Comparing base (1d81ea9) to head (6340fe0).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/fontless/src/vite.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #665      +/-   ##
==========================================
- Coverage   53.47%   53.40%   -0.08%     
==========================================
  Files          11       11              
  Lines         733      734       +1     
  Branches       93       93              
==========================================
  Hits          392      392              
- Misses        341      342       +1     

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[gioboa]

LGTM, Thanks