Add persistent storage feature

[cybcon]

Summary

This branch implements persistent storage for Modbus registers and related documentation, tests, and configuration updates. It adds a new persistence library, integrates persistence into the server shutdown flow (graceful save), updates examples and configuration to support persistence, and includes supporting documentation and community files.

Highlights

• Persistence: Adds a new persistence library and integrates it into the server to persist register state across restarts.
• Tests: Adds unit tests for the persistence library to validate behavior.
• Configuration: Adds persistence settings to the server configuration and example files.
• Docs & Community: Adds SECURITY, CODE_OF_CONDUCT, CONTRIBUTING, and arc42 architecture docs/diagrams.
• Maintenance: Minor logging, version bumps, and .gitignore improvements.

Key Changes (features & fixes)

• Persistence implementation: New library and integration

  • Added src/app/lib/register_persistence/__init__.py implementing register persistence and storage optimizations.
  • Integrated persistence into server shutdown to perform a graceful save (src/app/modbus_server.py).
  • Added persistence configuration to src/app/modbus_server.json and examples.

• Tests

  • Added tests/test_register_persistence.py to exercise the new persistence library.
  • Adjusted existing tests where necessary (tests/test_server.py, tests/__init__.py).

• Documentation & Project Files

  • Added security and community docs: SECURITY.md, CODE_OF_CONDUCT.md, CONTRIBUTING.md.
  • Architectural documentation and diagrams: arc42/architecture.md and diagram files under arc42/diagrams/.
  • README updates describing the persistence feature and other clarifications.

• Examples & Configuration

  • Updated examples/test.json, examples/abb_coretec_example.json, and examples/udp.json (removed deprecated fields, enabled debug in test examples, and added persistence-related configuration where applicable).

• Build / CI / Packaging

  • Updated .github/workflows/test.yaml and Dockerfile variants for version changes and compatibility.

• Other fixes

  • Logger configuration and wording fixes in various docs.
  • Updated .gitignore to ignore virtual envs and envrc.
  • Removed src/app/__init__.py (file deletion).

Files of interest

• src/app/lib/register_persistence/__init__.py — new persistence library
• src/app/modbus_server.py — integrated persistence and graceful-save adjustments
• src/app/modbus_server.json — new/updated persistence configuration
• tests/test_register_persistence.py — new tests
• examples/test.json — example updated to reflect debug/persistence config
• SECURITY.md, CODE_OF_CONDUCT.md, CONTRIBUTING.md — new repository-level docs
• arc42/architecture.md and arc42/diagrams/ — architecture documentation and diagrams

Testing & Validation

• Run the test suite locally:

cd src/
pip install -r requirements.txt
pytest

• Run a focused test for persistence:

pytest tests/test_register_persistence.py -q

Migration / Configuration Notes

• Persistence is controlled via modbus_server.json. If upgrading from a branch without persistence, check persistence settings in src/app/modbus_server.json and the example files.
• The server now attempts to save register state during graceful shutdown — ensure your deployment allows the process time to shutdown cleanly.

Backward compatibility & Caveats

• Default behaviour remains unchanged if persistence is not enabled in the configuration. When enabled, the server will create/modify on-disk persistence files as configured.
• The branch introduces minor API/behaviour changes only around persistence lifecycle and storage optimization; existing Modbus protocol handling is not modified except for the persistence lifecycle integration.