feature: BGP server, FSM, Adj-RIB-In actor, and integration tests

- Implement passive-side BGP FSM (OpenSent → OpenConfirm → Established)
  with hold timer, keepalive timer, and NOTIFICATION on expiry
- Add bgp-server crate: config validation, TCP listener accept loop
  (BgpServerBuilder → BgpServer), connection dispatch
- Add bgp-rib crate: Adj-RIB-In actor owning route state with event
  broadcast for streaming consumers and snapshot for introspection
- Wire Adj-RIB-In into FSM: announce/withdraw on UPDATE for both legacy
  IPv4 NLRI fields and MP_REACH/MP_UNREACH path attributes
- Add bgp-integration-tests crate with 15 end-to-end tests covering
  session establishment, timers, UPDATE handling, and RIB introspection
- Fix require_empty! macro bug in open.rs (checked wrong buffer)
- Fix FourByteAsn capability parser returning consumed buffer as remainder
- Fix tracing subscriber not being installed in TracingArgs::install
- Expand docs/RFCs.md with full implementation status across 15 RFCs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/server/Cargo.toml

@@ -3,7 +3,12 @@ name = "bgp-server"
 edition.workspace = true
 
 [dependencies]
+bgp-packet.workspace = true
+bgp-primitives.workspace = true
+bgp-rib.workspace = true
+bytes.workspace = true
 clap.workspace = true
+futures.workspace = true
 eyre.workspace = true
 prometheus.workspace = true
 tokio.workspace = true