feat: implement run task (#1115)

### Changes are visible to end-users: yes

- Searched for relevant documentation and updated as needed: yes
- Breaking change (forces users to change their own code or config): no
- Suggested release notes appear below: yes

Implements an `aspect run` verb for executing runnable targets

### Test plan

- New test cases added

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Co-authored-by: Claude <noreply@anthropic.com>