Rework the speaker: sans-I/O FSM, sharded table, RFC 7606, ADD-PATH

The work of the speaker-cleanup branch as one commit; the branch keeps
the step-by-step history.

Sessions
- The state machine is a pure function from events to actions, driven by
  one task per connection. Idle, Connect and Active belong to a dialer
  that keeps configured peers up with backoff.
- Capabilities are negotiated: address families, four-octet AS numbers
  with AS_TRANS and AS4_PATH, route refresh, ADD-PATH per family and
  direction.
- Collision detection per RFC 4271 section 6.8, by address and
  identifier.
- Connections are taken only from configured peers, a few per address.
- A panic in a session is contained and answered with a Cease; a core
  task that stops shuts the server down with a Cease to every peer.
- Writes that make no progress are given up (RFC 9687).

Codec
- Malformed UPDATEs are handled as RFC 7606 says: treat-as-withdraw,
  attribute discard, or session reset, with the NOTIFICATION to send.
- Address families are open types; any can be named and ignored.
- Prefixes are fixed-size values, normalised, with path identifiers.
- Lengths are filled in after writing; one definition of each type code.
- Property tests and fuzz targets for every decoder.

Routing table
- Adj-RIBs-In and Loc-RIB in one sharded table that sessions write to
  directly. Routes are sixteen bytes; attribute sets are interned in
  wire form. Best-path selection per RFC 4271 section 9.1.2.2 with
  deterministic MED.
- A journal per shard lets followers read changes at their own pace;
  one that falls behind is resynchronised.
- On a RIPE RIS dump of 148 peers and 39.3M routes: loaded in 2.0 s on
  12 cores, about 52 bytes a route.

Announcing
- Originated routes come from the configuration. Each session has its
  own exporter with an Adj-RIB-Out, so a slow peer delays only itself.
- Routes to a peer in our own AS have an empty path and a LOCAL_PREF.

Operations
- HTTP status page, JSON API, event stream and Prometheus metrics.
- Benchmarks on synthetic and real tables.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/bench/Cargo.toml

@@ -0,0 +1,42 @@
+[package]
+name = "bgp-bench"
+description = "Benchmarks at the scale of the Internet routing table"
+authors.workspace = true
+edition.workspace = true
+homepage.workspace = true
+license.workspace = true
+repository.workspace = true
+version.workspace = true
+publish = false
+
+[dependencies]
+bgp-packet.workspace = true
+bgp-primitives.workspace = true
+bytes.workspace = true
+flate2 = "1"
+stats_alloc = { version = "0.1.10", optional = true }
+
+[dev-dependencies]
+bgp-integration-tests.workspace = true
+bgp-rib.workspace = true
+bgp-server.workspace = true
+tokio.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+
+[features]
+# Counts every allocation, to report how much memory a table holds. The
+# counters are shared by all threads and slow them down, so timings are
+# taken without this and memory is measured in a run of its own.
+count-memory = ["dep:stats_alloc"]
+
+[[bench]]
+name = "full_table"
+harness = false
+
+[[bench]]
+name = "real_table"
+harness = false
+
+[lints]
+workspace = true