feat: add otel logger injection

[wangyb-A]

Issue #, if available: #

Description

• Add a wrap_logger hook to DurableInstrumentationPlugin and chain it in PluginExecutor.wrap_logger.
• Wire logger wrapping into DurableContext.set_logger, and trigger it once on the root context in durable_execution. Child contexts inherit the already-wrapped logger; wrapping is idempotent.
• New OtelEnrichedLogger that injects the active span context into each log extra.
• Plugin resolves the correct span via get_current_span_context: the active operation span inside a step/child context, the enclosing operation span between steps, and the invocation span (from the registry) at the top level.
• on_user_function_end now restores the enclosing operation span (parent_id) rather than always the invocation span, so between-step logs inside a child context correlate to that child context.

Testing

• Unit test
• Example logging:

// Top level → invocation span
{
  "level": "INFO", "message": "Workflow started", "logger": "root",
  "otel.trace_id": "6a288a880695a2d879ef07517e60531b",
  "otel.span_id":  "bbe5fdb86682dac4",
  "otel.trace_sampled": true
}

// Inside top-level step "top-greet" → step span
{
  "level": "INFO", "message": "Greeting inside step", "logger": "root",
  "operationName": "top-greet", "attempt": 1, "greeting_name": "world",
  "otel.trace_id": "6a288a880695a2d879ef07517e60531b",
  "otel.span_id":  "796a9b22593b6959",
  "otel.trace_sampled": true
}

// Inside child context (between steps) → child-context span
{
  "level": "INFO", "message": "Entering child context", "logger": "root",
  "parentId": "c5faca15...3947e6",
  "otel.trace_id": "6a288a880695a2d879ef07517e60531b",
  "otel.span_id":  "be02ea8c17bd3715",
  "otel.trace_sampled": true
}

// Inside nested step "child-greet" → nested step span
{
  "level": "INFO", "message": "Greeting inside step", "logger": "root",
  "operationName": "child-greet", "attempt": 1, "greeting_name": "nested",
  "otel.trace_id": "6a288a880695a2d879ef07517e60531b",
  "otel.span_id":  "67fdcf54688f3644",
  "otel.trace_sampled": true
}

[wangyb-A]

Currently, on_invocation_start is running on main thread (instead of worker thread). So, even if we attach the span to the context, it's invisible for worker thread.