Issue #, if available: #120

Description of changes:

Replaces the single catch-all CallableRuntimeError with a typed, per-operation error hierarchy. A failed step, invoke, child context, or wait_for_condition now surfaces as a distinct, catchable exception type. It also lands the from_exception/throw_if_error changes those types require. The CallbackError rework and the nested-boundary regression test are intentionally deferred to follow-up PRs.

Breaking changes

• Operation failures now raise the typed subclasses (StepError, InvokeError, ChildContextError, WaitForConditionError) instead of CallableRuntimeError (removed).
• Catch on the exception class to identify the operation. The error_type attribute carries the original Python exception name (e.g. "ValueError"); the original message is on .message, and the original error is attached as cause (the live exception on first run, a reconstructed stand-in on replay). At the wire/checkpoint level, an escaping wrapper is recorded under its class-name discriminator (e.g. "StepError") one level up, while the operation's own FAIL checkpoint records the raw error type.
• wait_for_condition check failures are now wrapped in WaitForConditionError rather than re-raised raw.
• wait_for_callback/callback failures now surface as CallbackError (previously CallableRuntimeError); CallbackError remains in the termination tree until the follow-up.
• An exhausted interrupted step fails immediately as StepError rather than round-tripping through a Lambda retry.

Testing

• Updated/added unit tests across exceptions, lambda_service, state, concurrency, and the four operation handlers.
• Added coverage for: registry + from_error_fields (including fallback), from_exception field preservation across a single operation boundary, raise_operation_error, wait_for_condition control-flow errors propagating unwrapped, and the execution result recording the StepError discriminator while the step's own FAIL checkpoint records the raw error type.
• Added an integration test and an example; the example also verifies the caught error is identical across a wait/replay boundary.

Follow-ups

• Move CallbackError under DurableOperationError with graded subclasses (CallbackExternalError, CallbackTimeoutError, CallbackSubmitterError) and drop CALLBACK_ERROR metadata.
• Regression test for data surviving ≥2 nested run_in_child_context boundaries

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