feat(database): add oracle provider integration via python-oracledb

[david-mamani]

Description
This Pull Request implements support for Oracle Database as a storage provider for MemU, addressing the requirements for Track D (External Tool / Database Integration) and Issue #168.

The implementation utilizes the python-oracledb driver in Thin mode to ensure lightweight connectivity without requiring Oracle Instant Client binaries. The architecture strictly follows the design patterns established by the existing PostgreSQL provider to ensure code consistency and maintainability, leveraging SQLAlchemy and SQLModel for typed database interactions.

Technical Implementation

• Core Logic: Introduced the memu.database.oracle package, including OracleStore and specific repositories (OracleResourceRepo, OracleMemoryItemRepo).
• Factory Registration: Updated src/memu/database/factory.py to recognize the oracle provider configuration.
• Testing Strategy: Added a comprehensive mock-based unit test suite (tests/test_oracle_mock.py). This validates the connection flow, session management, and CRUD operations within the CI/CD environment without requiring a live Oracle instance, ensuring verifiable logic stability.
• Documentation: Included docs/oracle_integration.md to provide isolated installation and configuration instructions without modifying the main README to avoid conflicts.

How to Test
The integration includes a validation script that mocks the database engine, allowing verification of the driver logic and repository flow:

1. Install the required dependency:
   uv add oracledb

2. Run the verification suite:
   uv run pytest tests/test_oracle_mock.py

Resolves #168

[Jununn]

Hi, the build for this PR is not passing yet. Please make the necessary updates, and we’ll review again after that. Thanks! @david-mamani

[ankaisen]

I recommend we do not add oracledb as a default (hard) dependency of the base package. It's fine to keep this as an optional dependency (extra) so only Oracle users pull it in, e.g. pip install memu-py[oracle].

[david-mamani]

I've refactored pyproject.toml to make oracledb an optional dependency and implemented lazy loading in the source code. Tests are passing locally without the driver installed.