Add `@protected` onto `execute` on `Conditional`s

### Describe the bug

The `execute` function should be `@protected` in all `Conditional` objects, only called by `Always` execution. Some of them are missing and should be added so that the APIs are more clear to users and so they don't accidentally use a function in the wrong context.

### To Reproduce

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### Expected behavior

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### Actual behavior

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### Additional: Dart SDK info

_No response_

### Additional: pubspec.yaml

```yaml

```

### Additional: Context

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