Implement SHA256 authentication for Fronius firmware 1.38.6-1+

[Copilot]

Fronius firmware version 1.38.6-1 changed the login encryption from MD5 to SHA256. This PR implements version-dependent authentication to support both old and new firmware versions.

Changes Made

Core Authentication Updates

• Enhanced hash_utf8() function: Added algorithm parameter supporting both "MD5" and "SHA256" with backward-compatible MD5 default
• Updated get_auth_header() method: Now uses version-appropriate algorithm from API config and includes correct algorithm in digest auth header
• Extended FroniusApiConfig dataclass: Added auth_algorithm field with MD5 default for backward compatibility

Version Configuration

• Split API configuration: Updated the last config range to create a boundary at firmware 1.38.6-1
  • Versions < 1.38.6-1: Continue using MD5
  • Versions ≥ 1.38.6-1: Use SHA256
• Preserved existing behavior: All firmware versions before 1.38.6-1 maintain identical authentication behavior

Testing

• Comprehensive test suite: Added 8 new test cases covering boundary conditions, algorithm selection, and hash function behavior
• Regression testing: All existing tests continue to pass, ensuring no breaking changes

Example Usage

# Firmware 1.37.0 automatically uses MD5
config_old = get_api_config(version.parse("1.37.0"))
print(config_old.auth_algorithm)  # "MD5"

# Firmware 1.38.6-1+ automatically uses SHA256  
config_new = get_api_config(version.parse("1.38.6-1"))
print(config_new.auth_algorithm)  # "SHA256"

# Hash function supports both algorithms
hash_utf8("test", "MD5")     # 32-character MD5 hex digest
hash_utf8("test", "SHA256")  # 64-character SHA256 hex digest

The implementation maintains full backward compatibility while adding support for the new SHA256 authentication requirement in newer firmware versions.

Fixes #178.

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[MaStr]

This fix needs some more changes.
It seems that the change needs a two step approach.

Old passwords needs to be hashed with MD5.
Newer passwords with sha256.

On the same time the complete digest needs to be sha256 now.

[Copilot]

Pull Request Overview

Implements version-dependent SHA256 authentication for Fronius firmware 1.38.6-1+ while maintaining backward compatibility with MD5 for older versions. The authentication method is automatically selected based on firmware version.

• Enhanced authentication system with algorithm parameter supporting both MD5 and SHA256
• Split API configuration to handle version-specific authentication requirements
• Added comprehensive test coverage for authentication boundary conditions

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/batcontrol/inverter/fronius.py	Core authentication implementation with enhanced hash function, API config updates, and multi-method login logic
tests/batcontrol/inverter/test_fronius_auth.py	Comprehensive test suite covering hash algorithms, version boundaries, and authentication behavior

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