[Do not review] Update build configuration for e2e tests

[AmelBawa-msft]

Summary of the Pull Request

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

This PR updates the Windows wslc end-to-end (e2e) test build configuration to optionally use CMake unity builds for faster recompiles, and enables that mode in the CI build pipeline.

Changes:

• Add WSL_E2E_UNITY_BUILD + batching logic to unity-build only the test/windows/wslc/e2e/*.cpp sources via UNITY_BUILD_MODE GROUP.
• Enable -DWSL_E2E_UNITY_BUILD=ON in .pipelines/build-job.yml so CI uses unity builds for these e2e sources.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/windows/wslc/CMakeLists.txt	Introduces an opt-in unity build mode for wslc e2e test sources, grouping them into unity batches.
.pipelines/build-job.yml	Enables the new WSL_E2E_UNITY_BUILD option in CI by passing it to the CMake configure step.