Python: Add OpenTelemetry integration for GitHubCopilotAgent (#5142)

* Python: Add OpenTelemetry integration for GitHubCopilotAgent

- Split GitHubCopilotAgent into RawGitHubCopilotAgent (core, no OTel) and
  GitHubCopilotAgent(AgentTelemetryLayer, RawGitHubCopilotAgent) with tracing
- Add default_options property to expose model for span attributes
- Export RawGitHubCopilotAgent from all public namespaces
- Add github_copilot_with_observability.py sample and update README

* Python: Fix OTEL_SERVICE_NAME default in GitHub Copilot README

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Python: Add unit tests for RawGitHubCopilotAgent.default_options property

* Python: Address review feedback on GitHubCopilotAgent OTel integration

- Add middleware param to GitHubCopilotAgent.run() overloads so per-call
  middleware is explicitly forwarded through AgentTelemetryLayer
- Remove github_copilot_with_observability.py sample per feedback; replace
  with inline snippet + link to observability samples in README

* Python: Address review feedback on log_level and session kwargs typing

- Add middleware param to RawGitHubCopilotAgent.run() overloads for interface
  compatibility with AgentTelemetryLayer
- Fix import in README observability snippet to use agent_framework.github

* Python: Add AgentMiddlewareLayer to GitHubCopilotAgent MRO

Follow FoundryAgent pattern: AgentMiddlewareLayer runs outside the telemetry
span so middleware execution time is not captured in traces. Overloads removed
as AgentMiddlewareLayer.run() handles dispatch via MRO.

* Python: Add explicit __init__ to GitHubCopilotAgent for auto-complete and docstrings

* Python: Address review feedback on middleware warning and test assertions

- Add assert "timeout" not in opts to test_default_options_includes_model_for_telemetry
  to document the intentional asymmetry where timeout is extracted into _settings
  and not returned in default_options.
- Replace silent del middleware with a logged warning when per-run middleware is
  passed to RawGitHubCopilotAgent, making it clear that the GitHub Copilot SDK
  handles tool execution internally and chat/function middleware cannot be injected.

* Python: Use Self for __aenter__ return type in RawGitHubCopilotAgent

Address review feedback: use typing.Self (3.11+) / typing_extensions.Self
(3.10) for __aenter__ so subclasses like GitHubCopilotAgent get the correct
return type from async context manager usage.

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

python/packages/github_copilot/tests/test_github_copilot_agent.py

@@ -189,6 +189,31 @@ class TestGitHubCopilotAgentInit:
             "content": "Direct instructions",
         }
 
+    def test_default_options_includes_model_for_telemetry(self) -> None:
+        """Test that default_options merges model from settings for AgentTelemetryLayer span attributes."""
+        agent: GitHubCopilotAgent[GitHubCopilotOptions] = GitHubCopilotAgent(
+            default_options={"model": "claude-sonnet-4-5", "timeout": 120}
+        )
+        opts = agent.default_options
+        assert opts["model"] == "claude-sonnet-4-5"
+        assert "timeout" not in opts  # timeout is extracted into _settings, not returned in default_options
+
+    def test_default_options_without_model_configured(self) -> None:
+        """Test that default_options works correctly when no model is configured."""
+        agent = GitHubCopilotAgent(instructions="Helper")
+        opts = agent.default_options
+        assert "model" not in opts
+        assert opts.get("system_message") == {"mode": "append", "content": "Helper"}
+
+    def test_default_options_returns_independent_copy(self) -> None:
+        """Test that mutating the returned dict does not affect internal state."""
+        agent: GitHubCopilotAgent[GitHubCopilotOptions] = GitHubCopilotAgent(
+            default_options={"model": "gpt-5.1-mini"}
+        )
+        opts = agent.default_options
+        opts["model"] = "mutated"
+        assert agent._settings.get("model") == "gpt-5.1-mini"
+
 
 class TestGitHubCopilotAgentLifecycle:
     """Test cases for agent lifecycle management."""