feat: Add ReadFrom parsing support to ConfigurationOptions for AZ Affinity

[jbrinkman]

Summary

This PR implements comprehensive ReadFrom parsing support in ConfigurationOptions to enable AZ (Availability Zone) affinity configuration through connection strings and programmatic configuration. This addresses issue #26 by providing a complete implementation of ReadFrom strategy parsing, validation, and serialization.

Changes Made

Core Implementation

• ReadFrom Parsing: Added support for parsing readFrom and az parameters from connection strings
• Strategy Validation: Implemented comprehensive validation for ReadFromStrategy and AZ parameter combinations
• Serialization Support: Added ToString formatting for ReadFrom configurations with round-trip integrity
• Property Validation: Enhanced ReadFrom property setter with cross-validation logic
• Error Handling: Comprehensive error messages and validation throughout the pipeline

Supported ReadFrom Strategies

• Primary - Always read from primary nodes
• PreferReplica - Prefer replica nodes, fallback to primary
• AzAffinity - Prefer replicas in the same AZ, with fallback
• AzAffinityReplicasAndPrimary - Prefer nodes in the same AZ (replicas first, then primary), with fallback

Connection String Examples

localhost:6379,readFrom=Primary
localhost:6379,readFrom=PreferReplica  
localhost:6379,readFrom=AzAffinity,az=us-east-1a
localhost:6379,readFrom=AzAffinityReplicasAndPrimary,az=eu-west-1b

Test Coverage

• 992 lines of comprehensive end-to-end integration tests
• 48 test cases covering complete configuration pipeline
• Connection string parsing to FFI layer verification
• Error handling and validation scenarios
• Round-trip serialization integrity
• Backward compatibility with legacy configurations
• Performance testing with concurrent connections
• Both standalone and cluster client scenarios

Technical Details

Implementation Approach

1. Connection String Parsing: Extended DoParse method to handle readFrom and az parameters
2. Validation Logic: Implemented ValidateAndSetReadFrom with comprehensive strategy/AZ validation
3. Serialization: Added FormatReadFrom method for ToString output with proper formatting
4. Property Validation: Enhanced ReadFrom property setter with immediate validation
5. Error Propagation: Ensured validation errors propagate correctly through the entire pipeline

Validation Rules

• Primary and PreferReplica strategies cannot have AZ parameters
• AzAffinity and AzAffinityReplicasAndPrimary strategies require non-empty AZ parameters
• Case-insensitive parsing for ReadFrom strategy values
• Comprehensive error messages for all validation scenarios

Backward Compatibility

• Existing configurations without ReadFrom continue to work unchanged
• Default behavior preserved when no ReadFrom is specified
• Legacy connection strings remain fully functional

Testing

All tests pass including:

• ✅ 48 new end-to-end integration tests
• ✅ Existing unit tests for ConfigurationOptions parsing
• ✅ Existing unit tests for ReadFrom property validation
• ✅ Integration tests for ConnectionMultiplexer ReadFrom mapping

Closes

Closes #26

Checklist

• Implementation follows existing code patterns and conventions
• Comprehensive test coverage with end-to-end integration tests
• Backward compatibility maintained
• Error handling and validation implemented
• Documentation through comprehensive test examples
• All existing tests continue to pass
• DCO signoff included in all commits

[edlng]

LGTM! I do agree with Yury's comment on cutting down the tests^

[Yury-Fridlyand]

I added true e2e tests, few tests were simplified and moved to UT.