Feature/upgrade pymodbus

[cybcon]

Summary

This PR upgrades the Modbus Server project to PyModbus v3.11 and includes several maintenance updates and improvements.

Key Changes

Dependency Upgrades

• PyModbus v3.11: Major version upgrade with updated API and imports
  • Changed from pymodbus.server.sync to pymodbus.server module imports
  • Updated datastore imports: removed deprecated ModbusSlaveContext, now using ModbusDeviceContext
  • Updated device module path: pymodbus.device → pymodbus.pdu.device
  • Adjusted function signatures and data block handling to match new API

Infrastructure Updates

• Alpine base image: Updated from 3.23.2 to 3.23.3 (security & patch updates)
• Version bump: 1.4.1 → 2.0.0 (reflects major PyModbus upgrade)
• Copyright year: Updated to 2026

Feature Removals

• Removed zeroMode configuration: The deprecated zeroMode option has been removed from both the configuration file and the codebase. This simplification aligns with PyModbus v3.11 standards and reduces unnecessary complexity.

Documentation & CI/CD Improvements

• CI/CD workflow enhancement: Updated GitHub Actions test workflow to install dependencies from dedicated tests/requirements.txt file, improving setup clarity and maintainability
• Improved configuration handling: Updated default config file path logic for better portability
• Added Copilot Instructions: New .github/copilot-instructions.md with comprehensive project documentation including architecture, build commands, conventions, and configuration guidelines
• Updated documentation: README and code comments reflect new version and removed features

Code Quality

• Updated docstring format and type hints throughout modbus_server.py
• Enhanced error handling documentation

Files Changed

• .github/copilot-instructions.md (new)
• .github/workflows/test.yaml
• Dockerfile
• LICENSE
• README.md
• src/app/modbus_server.json
• src/app/modbus_server.py
• src/requirements.txt
• tests/requirements.txt

Testing

All changes are backward compatible with existing configurations (except for removal of zeroMode). The upgrade has been validated across Python 3.10, 3.11, and 3.12.