#459 HIGH: Performance - list() to tuple() conversions

Unnecessary list allocations: 1. list(dict.keys())[-1] -> tuple (inline_executor.py:690,893) 2. list(self._tools.keys()) -> tuple (registry.py:262,273) 3. list(reversed(...)) -> tuple (durable_context.py:1880) 4. list(spawned_tasks.keys()) -> tuple (operators.py:616) Impact: Memory savings, immutability signaling.