[WIP] Add tests for network packet processing chain

[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>test: Network packet processing chain</issue_title>
<issue_description>## Problem

Magma.Network is the core processing engine - delegate chaining, packet routing, error propagation. Completely untested.

Sub-tasks

• Create test/Magma.Network.Facts project, add to solution
• Single-delegate chain: packet in, processed packet out
• Multi-delegate chain: verify ordering, short-circuit behaviour
• Error propagation: exception in a delegate, verify chain halts or continues as designed
• IPacketTransmitter / IPacketReceiver mock implementations for isolation

Dependencies

Depends on: nothing (tests existing code)
Unlocks: #108 (UDP chain integration), #131 (Kestrel transport)

Phase

Phase 0 (Foundation) - can start immediately</issue_description>

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

• Fixes test: Network packet processing chain #104

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