Feat/587-circuit-relay (#611)

* feat: implemented setup of circuit relay and test cases

* chore: remove test files to be rewritten

* added 1 test suite for protocol

* added 1 test suite for discovery

* fixed protocol timeouts and message types to handle reservations and stream operations.

* Resolved merge conflict in libp2p/tools/utils.py by combining timeout approach with retry mechanism

* fix: linting issues

* docs: updated documentation with circuit-relay

* chore: added enums, improved typing, security and examples

* fix: created proper __init__ file to ensure importability

* fix: replace transport_opt with listen_addrs in examples, fixed typing and improved code

* fix type checking issues across relay module and test suite

* regenerated circuit_pb2 file protobuf version 3

* fixed circuit relay example and moved imports to top in test_security_multistream

* chore: moved imports to the top

* chore: fixed linting of test_circuit_v2_transport.py

---------

Co-authored-by: Manu Sheel Gupta <manusheel.edu@gmail.com>

libp2p/relay/__init__.py

@@ -0,0 +1,28 @@
+"""
+Relay module for libp2p.
+
+This package includes implementations of circuit relay protocols
+for enabling connectivity between peers behind NATs or firewalls.
+"""
+
+# Import the circuit_v2 module to make it accessible
+# through the relay package
+from libp2p.relay.circuit_v2 import (
+    PROTOCOL_ID,
+    CircuitV2Protocol,
+    CircuitV2Transport,
+    RelayDiscovery,
+    RelayLimits,
+    RelayResourceManager,
+    Reservation,
+)
+
+__all__ = [
+    "CircuitV2Protocol",
+    "CircuitV2Transport",
+    "PROTOCOL_ID",
+    "RelayDiscovery",
+    "RelayLimits",
+    "RelayResourceManager",
+    "Reservation",
+]