Allow passing --changed cli option to vitest

### Command

test

### Description

The `unit-test` builder does not provide a way to use the `--changed` vitest option: https://vitest.dev/guide/cli.html#changed. This will analyze the import graph and only run tests affected by a change, which is useful for running a subset of the test suite for pull requests. This option is not available through the vitest configuration file.

### Describe the solution you'd like

Add a `changed: ` option to the `unit-test` builder options which passes `--changed ` to the vitest runner.

### Describe alternatives you've considered

I don't think there are any good workarounds. Using `@analogjs/vitest-angular` exposes vitest directly, but requires more setup and is not an "official" package.

從單元測試建置器選項開始，追蹤它們如何傳遞給 Vitest runner。驗證變更後的字串選項會轉送 --changed ，並確保相關的建置器測試涵蓋產生的命令。

由索引模型根據 Issue 內容生成。