[Core] Give the OpenAI Realtime wire codec a reusable home (RFC #6592 P0a) (#7640)

Signed-off-by: psv666 <2693925048@qq.com>

vllm_omni/protocol/__init__.py

@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+"""Wire protocols vLLM-Omni speaks, independent of who serves or runs them.
+
+A module under ``vllm_omni.protocol`` describes *what is on the wire*: how a
+client payload is parsed and validated, and what shape a server payload has.
+It never decides how a request is executed, which model answers it, or where
+the session state lives. That keeps one protocol implementation usable by more
+than one runtime (see ``vllm_omni.protocol.realtime``).
+
+Dependency rule, asserted by ``tests/protocol/realtime/test_protocol_import_boundary.py``:
+nothing here may import ``vllm_omni.engine``, ``vllm_omni.entrypoints``,
+``vllm_omni.model_executor``, ``vllm_omni.worker`` or ``vllm_omni.clients``.
+The arrows point inwards --- those packages import the protocol, never the
+other way round.
+"""