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>

Cargo.toml

@@ -17,7 +17,9 @@ version = "0.0.2"
 # --- Our crates ---
 bgp-packet = { path = "crates/packet" }
 bgp-primitives = { path = "crates/primitives" }
+bgp-rib = { path = "crates/rib" }
 bgp-server = { path = "crates/server" }
+bgp-integration-tests = { path = "crates/integration-tests" }
 
 # --- General ---
 bitfield = "0.19.0"
@@ -36,3 +38,4 @@ prometheus = "0.14.0"
 protobuf = { package = "protobuf", version = "3.7.2" }
 protobuf-codegen = { package = "protobuf-codegen", version = "3.7.2" }
 clap = { version = "4.5.53", features = ["derive"] }
+futures = "0.3"