[feat][DurableContext] Use a blake2 to generate step_id

Feature:
- Replaces existing mechanism to produce durable operation ids with

Test Changes:
- Instead of testing manually the steps, we a/ produce a generator so
  that we can rely on next(_) to get the sequence
- We verify invariance over behaviour:
   - deterministic execution
   - identical generation for every new context
   - parent step id participates in the generation

Signed-off-by: Astraea Sinclair <[email protected]>

Author: FullyTyped

src/aws_durable_execution_sdk_python/context.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import hashlib
 import logging
 from typing import TYPE_CHECKING, Any, Concatenate, Generic, ParamSpec, TypeVar
 
@@ -220,9 +221,10 @@ def _create_step_id(self) -> str:
         the id generated by this method. It is subject to change without notice.
         """
         new_counter: int = self._step_counter.increment()
-        return (
+        step_id = (
             f"{self._parent_id}-{new_counter}" if self._parent_id else str(new_counter)
         )
+        return hashlib.blake2b(step_id.encode()).hexdigest()[:64]
 
     # region Operations