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/samples/02-agents/providers/github_copilot/README.md

@@ -24,6 +24,22 @@ The following environment variables can be configured:
 | `GITHUB_COPILOT_TIMEOUT` | Request timeout in seconds | `60` |
 | `GITHUB_COPILOT_LOG_LEVEL` | CLI log level | `info` |
 
+## Observability
+
+`GitHubCopilotAgent` has OpenTelemetry tracing built-in. To enable it, call `configure_otel_providers()` before running the agent:
+
+```python
+from agent_framework.observability import configure_otel_providers
+from agent_framework.github import GitHubCopilotAgent
+
+configure_otel_providers(enable_console_exporters=True)
+
+async with GitHubCopilotAgent() as agent:
+    response = await agent.run("Hello!")
+```
+
+See the [observability samples](../../../02-agents/observability/) for full examples with OTLP exporters.
+
 ## Examples
 
 | File | Description |