🪲 BUG-#204: Replace unsafe ctypes memory access in StorageDefault

[FernandoCelmer]

Description

Replace ctypes.cast(id, py_object) with a safe dict-based in-memory storage in StorageDefault.

Issue: 📌 ISSUE-#204

Changes

• post() — now stores context in _store dict (was no-op returning None)
• get() — retrieves from dict, returns Context() for missing keys (was ctypes.cast on memory address)
• key() — returns f"{workflow_id}-{task_id}" consistent with S3/GCS/File (was id() memory address)
• Removed ctypes import
• Updated tests with roundtrip, missing key, and key format assertions

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes