Add basic high-level SDK for cmd_vel using Go2 ethernet

Implement basic high-level SDK support for cmd_vel control using Unitree Go2's ethernet connection (as opposed to WebRTC).

**Tasks:**

* Implement ethernet-based cmd_vel interface
* Test with Go2
* Document SDK usage
* Add to appropriate blueprints

**Context:** Prerequisite for whole body controller work on Go2.

---
*Synced from* [DIM-755](https://linear.app/dimensional/issue/DIM-755)