Add uProtocol Rust tutorial

[nsengupta]

Description

Add a hands-on uProtocol tutorial for the Rust SDK.

The tutorial takes the reader through three progressive phases:

1. Raw Unix Domain Sockets and manually framed uProtocol messages.
2. uProtocol L1/L2 abstractions over the same transport.
3. Zenoh as the transport, demonstrating multi-subscriber fan-out.

The tutorial is designed for developers who are new to uProtocol and want to
understand the relationship between the wire format, uProtocol abstractions,
and transport implementations.

All three phases include runnable Rust examples and accompanying narrative.

Validation

• cargo clippy --all-targets --all-features — passed for all phases
• Phase 2 tests — passed
• Phase 1 publisher/subscriber demo — verified
• Phase 2 publisher/subscriber demo — verified
• Phase 3 publisher and both subscribers — verified
• ./tools/fmt_clippy_doc.sh — passed for up-rust