feat(network): NetworkGraph types + extractor (Track D commit 2/6)

[avrabe]

Summary

Track D commit 2 of 6 for v0.8.0 — adds the typed network graph that
bridges the AADL SystemInstance and the upcoming WCTT analysis.

• crates/spar-network/src/types.rs — NetworkNode, NetworkLink,
  SwitchType (FIFO / Priority / TSN), NetworkGraph with nodes,
  links, switches, end_stations, and reachable_from accessors.
  Phase 1 classifies TSN switches but treats them as opaque; full
  TSN-shaped service curves arrive with the Spar_TSN property set in
  Phase 2.
• crates/spar-network/src/extract.rs — walks SystemInstance,
  classifies buses by Spar_Network::Switch_Type, registers the
  devices/processors connected to each switched bus as end stations,
  and emits one NetworkLink per bus-touching connection. Each link
  carries Output_Rate, Forwarding_Latency, and Queue_Depth from
  the bus, using a typed-first / string-fallback property accessor
  pattern that mirrors spar-analysis::property_accessors.
• crates/spar-network/tests/extract_tests.rs — 6 integration tests
  driving small inline AADL fixtures: simple FIFO topology, Priority
  switch classification, opaque TSN switch (with link annotations
  still propagating), unannotated-bus skip, range latency lowering,
  and graph reachability.
• New rivet artifacts: REQ-NETWORK-004 (network graph extraction)
  and TEST-SPAR-NETWORK-GRAPH (the new integration tests).

What is intentionally out of scope

• No Network Calculus primitives — that's Track D commit 3.
• No wctt.rs analysis pass — Track D commit 4.
• No Lean theorems — Track D commit 5.
• No latency.rs integration or COMPLIANCE.md update — Track D commit 6.

Links

• Closes a piece of Track D: TSN/Ethernet WCTT analysis with first-class switch modeling #149.
• Design: docs/designs/track-d-tsn-wctt-research.md §5.4 / §6.1.
• Builds on feat(network): Spar_Network property set + spar-network crate skeleton (Track D commit 1/6) #155 (Spar_Network property set + crate skeleton).

Test plan

• cargo build --workspace clean
• cargo test -p spar-network — 18 tests green (12 unit + 6 integration)
• cargo test -p spar-hir-def — 429 tests green (no regression)
• cargo test --workspace — all crates green
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo fmt --all -- --check clean
• rivet validate — Result: PASS

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 76.88442% with 92 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spar-network/src/extract.rs	72.13%	90 Missing ⚠️
crates/spar-network/src/types.rs	97.33%	2 Missing ⚠️

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