Implemented handshake and heartbeat

Implemented handshake in json server and handoff to endpoint

Endpoint handles connector handshake accept/decline then launches both
its IO threads alongside its heartbeat thread which contains simple
timeout logic, timeout calls connection handles to close, subsequently
killing the endpoint

src/dynalab_core/constants.py

@@ -2,7 +2,18 @@
 # Copyright (C) 2026 Association Exergie <association.exergie@gmail.com>
 # SPDX-License-Identifier: GPL-3.0-or-later
 
+from uuid import uuid4
 from dynalab_core.protocols.common import VersionDescriptor
+from dynalab_core.protocols.constants import PROTOCOL_VERSION
+from dynalab_core.protocols.packets.handshake import DynaLabHello
 
 
 CORE_VERSION = VersionDescriptor(type="alpha", major=0, minor=0, patch=1)
+
+HELLO_PACKET = DynaLabHello(
+    instance_id=uuid4(),
+    core_version=CORE_VERSION,
+    protocol_version=PROTOCOL_VERSION,
+    heartbeat_interval_ms=1000,
+    heartbeat_timeout_ms=5000,
+)