Introduce the Ethernet transport layer

**Description**
Add support for an Ethernet-based transport layer to enable communication with remote boards/devices over wired networks.

**Motivation**
The current transport system lacks Ethernet support. Adding this layer will enable communication with devices connected via Ethernet, which is currently unsupported.

**Requirements**
Support for Arduino boards equipped with an Ethernet shield (e.g., W5100/W5500-based modules).

**Notes**
Ethernet transport operates over TCP, similarly to Wi-Fi. The implementation may reuse or alias existing Wi-Fi transport abstractions with minimal changes. It may also involve renaming shared components for clarity.

**API Changes**
None. This is an additive feature that does not affect existing APIs.