[WIP] Integrate UDP into Magma.Network processing pipeline

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>UDP: delegate chain integration</issue_title>
<issue_description>## Problem

Wire UDP into the Magma.Network processing pipeline so it's usable end-to-end.

Sub-tasks

• Register UDP handler in the delegate chain (protocol number 17)
• Bidirectional: inbound demux and outbound frame construction
• Integration test: full stack from raw Ethernet frame through to UDP payload delivery

Dependencies

Depends on: #107, #104 (chain tests provide confidence)
Unlocks: #124 (UDP sample app), #131 (Kestrel integration), #137 (API docs)

Phase

Phase 1 (Core Protocol & Tooling)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes UDP: delegate chain integration #108

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