feat: modernization phase 3 PR3

[dsmurfin]

No description provided.

[Copilot]

Pull request overview

This PR continues the modernization work by converting sACNDiscoveryReceiver from a GCD/delegate-based receiver to a Swift Concurrency actor pinned to the shared NIO event loop, exposing discovery/events/debug output via AsyncStreams and adding characterization + gated loopback tests.

Changes:

• Refactor sACNDiscoveryReceiver into an actor with async lifecycle/mutation APIs and AsyncStream outputs (discovery, events, debugLog), including a lifecycle “busy” gate (receiverBusy) and NIO scheduled heartbeat.
• Remove the discovery receiver delegate protocol and update docs/README to reflect the new actor/stream-based API.
• Add packet fixtures and new tests (seam-based characterization + gated end-to-end loopback) for paged assembly, malformed packet logging, and source-loss behavior.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Tests/sACNKitTests/PacketFixtures.swift	Adds a universe-discovery packet builder fixture for injection-based discovery testing.
Tests/sACNKitTests/DiscoveryReceiverTests.swift	Adds seam-based characterization tests plus an env-gated loopback test for actor-path inbound delivery.
Sources/sACNKit/Receiver/sACNReceiver.swift	Adds receiverBusy validation error for in-flight lifecycle/reconfiguration operations.
Sources/sACNKit/Receiver/sACNDiscoveryReceiver.swift	Converts discovery receiver to an actor with async lifecycle, stream outputs, scheduled heartbeat, and test seams.
Sources/sACNKit/Receiver/DiscoveryReceiverSource.swift	Removes dead lastNotifiedUniverseCount state from discovery source tracking.
Sources/sACNKit/Receiver/Delegate/sACNDiscoveryReceiverDelegate.swift	Deletes the delegate protocol now superseded by AsyncStream outputs.
Sources/sACNKit/Documentation.docc/sACNKit.md	Updates package overview to reflect sACNDiscoveryReceiver as an actor with streams.
README.md	Updates public-facing usage docs and adds an actor/stream example for discovery receiver.
docs/modernization/phase-4.md	Updates Phase 4 PR3 notes with completed implementation details and testing coverage.
AGENTS.md	Updates repo structure notes to reflect discovery receiver’s actor/stream API.
.claude/rules/timing.md	Updates timing rules to reflect discovery receiver heartbeat running via NIO scheduled tasks.
.claude/rules/threading.md	Updates threading guidance to reflect discovery receiver no longer being a GCD receiver component.

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