...r setup
Error handling has been enhanced to provide more actionable feedback for common misconfigurations, such as an invalid `buildTarget` or a malformed test runner package.

Refactors the Vitest test runner to improve code organization and separation of concerns.
The browser-specific helper functions (`findBrowserProvider`, `normalizeBrowserName`, and `setupBrowserConfiguration`) are moved from the main `executor.ts` file into a new, dedicated `browser-provider.ts` file.
This cleanup allows the main executor to focus solely on its primary responsibility of managing the test execution lifecycle, while properly encapsulating the browser setup logic in a single, co-located file.

...building
The experimental unit-test builder will now pass through the `progress` option
to the build system if present. By default the `progress` value of the build
target will be used.