Refactor echo example to use optimal binding address

- Replaced hardcoded listen address with `get_optimal_binding_address` for improved flexibility.
- Imported address validation utilities in `echo.py` and updated `__init__.py` to include new functions.

examples/echo/echo.py

@@ -19,6 +19,11 @@ from libp2p.peer.peerinfo import (
     info_from_p2p_addr,
 )
 
+from libp2p.utils.address_validation import (
+    get_optimal_binding_address,
+    get_available_interfaces,
+)
+
 PROTOCOL_ID = TProtocol("/echo/1.0.0")
 MAX_READ_LEN = 2**32 - 1
 
@@ -31,8 +36,9 @@ async def _echo_stream_handler(stream: INetStream) -> None:
 
 
 async def run(port: int, destination: str, seed: int | None = None) -> None:
-    listen_addr = multiaddr.Multiaddr(f"/ip4/0.0.0.0/tcp/{port}")
-
+    # CHANGED: previously hardcoded 0.0.0.0
+    listen_addr = get_optimal_binding_address(port)
+    
     if seed:
         import random
 

libp2p/utils/__init__.py

@@ -15,6 +15,12 @@ from libp2p.utils.version import (
     get_agent_version,
 )
 
+from libp2p.utils.address_validation import (
+    get_available_interfaces,
+    get_optimal_binding_address,
+    expand_wildcard_address,
+)
+
 __all__ = [
     "decode_uvarint_from_stream",
     "encode_delim",
@@ -26,4 +32,7 @@ __all__ = [
     "decode_varint_from_bytes",
     "decode_varint_with_size",
     "read_length_prefixed_protobuf",
+    "get_available_interfaces",
+    "get_optimal_binding_address",
+    "expand_wildcard_address",
 ]