Summary

Implement UDP transport abstraction using common_system's IUdpClient interface for the StatsD exporter.

Parent Issue

• deps: Implement UDP and gRPC transport using common_system interfaces #273

Tasks

• Create udp_transport.h with abstract interface
• Implement stub_udp_transport for fallback
• Implement network_udp_transport using common::interfaces::IUdpClient
• Update statsd_exporter to use udp_transport factory
• Add unit tests for UDP transport

Acceptance Criteria

• UDP transport compiles with and without MONITORING_HAS_NETWORK_SYSTEM
• statsd_exporter uses real UDP when network_system is available
• Graceful fallback to stub when network_system unavailable