add data url css tests

[jantimon]

Adding a feature

This PR adds e2e tests for CSS Modules in Data URLs, a feature that was recently merged in PR #78040.

Why?

After the feature was merged, @dlehmhus reported an issue (#78096) where CSS Modules in Data URLs don't work properly in Server Components. These tests will help verify the functionality and serve as regression tests once the issue is fixed.

How?

• Added comprehensive e2e tests that verify both client and server component behavior with CSS Modules in Data URLs
• Tests ensure that class names are applied correctly and styles are rendered properly
• The tests covers base64-encoded CSS module data URLs

These tests don't fix the issue reported in #78096 but provide test coverage for the feature.

Current results:

webpack: Tests: 4 failed, 0 passed, 4 total
turbopack: Tests: 1 failed, 3 passed, 4 total

Relates to #78096

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 52fd06a

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 3993dc7

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer