[otel] Balance context attach and detach across plugin lifecycles

[zhongkechen]

Summary

Both OTel plugins call opentelemetry.context.attach() without retaining the returned token or calling detach(). This leaves a workflow, invocation, operation, or attempt span active after its intended scope has ended.

The test suites currently reset the OTel context around every test specifically because plugin state otherwise leaks between tests.

Evidence

• packages/aws-durable-execution-sdk-python-otel/src/aws_durable_execution_sdk_python_otel/execution_plugin.py, attaches around lines 218-221, 458, and 506-508
• packages/aws-durable-execution-sdk-python-otel/src/aws_durable_execution_sdk_python_otel/invocation_plugin.py, attaches around lines 565 and 620-622
• The autouse fixtures in tests/test_execution_plugin.py and tests/test_invocation_plugin.py state that the plugins attach spans without detaching and would otherwise leak context between tests

A focused runtime probe completes a non-terminal invocation and observes that trace.get_current_span() still returns the prior workflow span after on_invocation_end.

OpenTelemetry requirement

The Context specification defines attach as returning a token used to restore the previous context and states that every attach should have a corresponding detach:

https://opentelemetry.io/docs/specs/otel/context/#attach-context
https://opentelemetry.io/docs/specs/otel/context/#detach-context

Impact

• Auto-instrumented work after plugin cleanup can be parented to a stale span.
• Ended or abandoned spans can remain current across warm Lambda invocations.
• Log correlation may report stale trace and span identifiers.
• Nested operations overwrite context rather than managing a balanced scope.

Acceptance criteria

• Every context.attach() token owned by the plugin has a corresponding context.detach().
• Invocation cleanup restores the context that was active before plugin invocation start.
• User-function cleanup restores the exact enclosing context without accumulating stale scopes.
• Tests no longer require global context resets to hide plugin lifecycle leaks.
• Tests cover nested child contexts, multiple sequential steps, failures, and warm invocation reuse.