Propagate metric groups to cross-language resources

Flink Agents bound action metric groups to same-language resources, but Java-to-Python and Python-to-Java wrappers did not consistently forward that group to the underlying provider resource. Provider-owned metrics for chat models, embeddings, vector stores, MCP resources, latency, errors, and cache behavior could therefore miss the caller's action scope.

Added default metric-forwarding hooks to PythonResourceAdapter and PythonResourceWrapper, wired Java wrappers for Python-backed resources to forward their metric group, and added Python-side helpers that unwrap FlinkMetricGroup when binding Java resources while rejecting unsupported custom metric groups clearly.

• Makes cross-language Java/Python resource observability match same-language resource behavior.
• Preserves single-recorder metric ownership while forwarding the bound metric group into provider implementations.
• Improves production tracing for agent resources that need backend-specific dimensions such as service, endpoint, tenant, latency, errors, or cache behavior.

• Added Python coverage for Java resource wrappers, FlinkMetricGroup unwrapping, None forwarding, and unsupported metric-group rejection.
• Added Java coverage for PythonResourceAdapterImpl and Python chat model setup metric forwarding.
• PR validation covered focused pytest, Maven compile/test targets across api/plan/runtime, and the repository lint script.