fix: Prevent Unlisted CSS from being excluded in the build when using CSS preprocessor

[PortalCube]

Overview

Currently, the build function of viteBuilder determines whether a file is a CSS entrypoint by checking if its file extension ends with .css. As a result, Unlisted CSS using preprocessors like Sass are not built as CSS entrypoints and ignored during the build.

This PR updates the CSS entrypoint detection to use the group.type value and adds e2e tests for CSS entrypoints.

This is my first PR to an open-source project, so if there's anything I missed or did incorrectly, please let me know. Thanks!

Manual Testing

Please check the CSS entrypoint e2e tests I added to the PR.

Related Issue

This PR closes #1580.

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commit: 9ddeb25

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.15%. Comparing base (7c59e9d) to head (9ddeb25).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1590      +/-   ##
==========================================
+ Coverage   80.83%   81.15%   +0.31%     
==========================================
  Files         131      131              
  Lines        6679     6680       +1     
  Branches     1091     1094       +3     
==========================================
+ Hits         5399     5421      +22     
+ Misses       1269     1248      -21     
  Partials       11       11              

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