Add Optional SQLAlchemy Backend for Persistent Storage

[Amanbig]

Description

Currently, RunAPI uses an in-memory list-based storage as its database layer.
When SQLAlchemy is not installed, the code explicitly skips DB-related functionality.

This limits RunAPI’s usefulness for:

• Production-like environments
• Multi-process usage
• Persistent storage use cases

Proposal

Introduce optional SQLAlchemy support while keeping the current in-memory fallback.

Suggested Approach

• If sqlalchemy is installed:
  • Use SQLAlchemy models and sessions
  • Support SQLite out of the box
• If not installed:
  • Continue using the existing in-memory list storage
• Abstract storage behind a common interface

Benefits

• Enables persistent storage
• Keeps RunAPI lightweight by default
• Allows gradual adoption without breaking changes

Expected Outcome

• More flexible backend support
• Better real-world usability