fix: report suspends as PENDING to plugins

[yaythomas]

Closes #491

Problem

In the experimental OpenTelemetry plugin, a durable execution that suspends inside a child context (for example a child context that calls context.wait(...)) produced a false fault on the child-context span in X-Ray, with a recorded exception named TimedSuspendExecution. The execution behaved correctly. A suspend is normal durable control flow, not a failure.

Root cause

The producer in state.py wrap_user_function reported a suspend to instrumentation plugins using the concrete exception name:

ErrorObject(type=type(e).__name__, ...)  # "TimedSuspendExecution"

UserFunctionOutcome.from_error matched only the base class name (SuspendExecution), so the suspend fell through to FAILED instead of PENDING. Since TimedSuspendExecution is the type every timed wait raises, the PENDING branch was never reached for that case. The OTEL plugin then rendered FAILED as a span error, which X-Ray shows as a fault. Top-level waits are unaffected because a top-level suspend resolves to InvocationStatus.PENDING at the invocation level.

Change

• Add an internal PluginExecutor.on_user_function_suspend(start_info) that reports a PENDING outcome with no error, dispatched through the existing public on_user_function_end.
• Route the except SuspendExecution branch in wrap_user_function to it instead of fabricating an error.
• Simplify UserFunctionOutcome.from_error to map None to SUCCEEDED and any other error to FAILED, removing the fragile name match.

This is an internal change. The public plugin interface already exposes UserFunctionEndInfo.outcome and PENDING, so there is no public API change.

Testing

• New regression test test_wrap_user_function_suspend_reports_pending_outcome fails on main (FAILED vs PENDING) and passes with this change.
• New unit tests cover from_start_info_suspended, on_user_function_suspend, and the simplified from_error.
• Core SDK suite: 1276 passed. OTEL package suite: 48 passed. Typecheck clean. hatch fmt --check clean.

[ayushiahjolia]

On SuspendExecution, SDK calls CheckpointDurableExecution with STARTED, so we might want to keep this Started, and later it will emit completed from list of operations from backend.