Feature/bvll router discovery

[acedrew]

Summary

• Network-layer message channel: NetworkLayer now optionally forwards network messages (I-Am-Router-To-Network, Who-Is-Router, etc.) via a broadcast channel instead of silently dropping them. Opt-in via network_messages() before start().
• BBMD table reads: read_bdt() and read_fdt() exposed through AnyTransport and BACnetClient, allowing inspection of BBMD Broadcast Distribution Tables and Foreign Device Tables.
• Router discovery: who_is_router_to_network() broadcasts the request and collects I-Am-Router-To-Network responses for a configurable duration, returning structured RouterInfo results.
• Python bindings: New BdtEntry, FdtEntry, and RouterInfo types with full type stubs. All three new client methods are available from Python.
• Example: examples/python/bbmd_scanner.py demonstrates scanning for BBMDs and discovering routers on a live network.
• Integration test: Containerized bvll-test binary + Dockerfile for testing against a live multi-building campus network.

Test results

Validated against a podman-based campus network with two buildings, two BBMDs (bacpypes3-based ACL BBMDs), a cross-subnet router, and HVAC simulators:

Test	Result	Notes
cargo check	✅ Pass	All crates compile
cargo test	✅ Pass	All existing tests green
Read BDT from BBMD	✅ Pass	2 entries returned — both BBMDs (10.1.0.2, 10.2.0.2) with correct subnet masks
Read FDT from BBMD	✅ Pass	0 entries — expected, no foreign devices registered
Who-Is-Router-To-Network	✅ Pass	No routers on BIP subnet (simulator uses bacpypes3 virtual networks internally)
Who-Is-Router(net=1001)	✅ Pass	Correctly returns empty when network is handled internally

Campus network topology

Building 1 (10.1.0.0/24)          Building 2 (10.2.0.0/24)
├── BBMD1      10.1.0.2  ◄──BDT──► BBMD2      10.2.0.2
├── Simulator  10.1.0.10           ├── Simulator  10.2.0.10
└── Router     10.1.0.254 ────────── Router     10.2.0.254

Test plan

• cargo check passes
• cargo test passes
• Container integration test against live campus network (BDT, FDT, router discovery)
• Verify Python bindings via maturin develop and example script

🤖 Generated with Claude Code

[jscott3201]

I just saw this. I'm merging a bunch of fixes into dev and will probably push those to main. Let me see where these changes stand after those get into the dev branch. These might have been picked up in the pass I did last night.