* feat(phase3): implement P1 memory-efficient metric storage

- Add lock-free ring buffer with atomic operations for thread-safe metric storage
- Implement compact metric types optimized for memory efficiency
- Create time-series storage with configurable retention policies
- Build comprehensive metric storage system with background processing
- Add statistics tracking and memory footprint monitoring
- Include comprehensive test suite for all new components
- Update documentation with Phase 3 P1 completion status

* feat(phase3): implement P2 statistical aggregation functions

- Add online statistics algorithms for real-time computation
- Implement P² algorithm for quantile estimation without data storage
- Create moving window aggregators with time-based expiration
- Build comprehensive stream aggregator with outlier detection
- Add high-level aggregation processor for metric rule management
- Include Pearson correlation and advanced statistical functions
- Provide comprehensive test suite with thread safety validation
- Update documentation with Phase 3 P2 completion status

* feat(p3): implement configurable buffering strategies

- Add multiple buffering strategies (immediate, fixed-size, time-based, priority-based, adaptive)
- Implement buffer manager for coordinating different strategies
- Add configurable overflow policies and flush triggers
- Build comprehensive buffer statistics and performance monitoring
- Update documentation to reflect P3 completion (75% Phase 3 progress)

* feat(p4): implement lock-free data structures integration

- Add lock-free queue with Michael & Scott algorithm for minimal contention
- Implement zero-copy memory pool with thread-local caching for allocation efficiency
- Build SIMD-accelerated aggregation functions for vectorized metric processing
- Add cross-platform optimization support (AVX2/AVX512 for x64, NEON for ARM64)
- Complete Phase 3: Performance & Optimization (100% - 4/4 tasks)

* docs: update README.md with Phase 3 completion

- Add Phase 3 features: memory-efficient storage, statistical aggregation,
  configurable buffering, and lock-free data structures
- Include comprehensive usage examples for all new components
- Add performance benchmarks and SIMD/lock-free capabilities
- Update project structure with new optimization modules
- Highlight C++20 modern features and multi-core optimizations

* fix(optimization): resolve CI/CD build errors

- Add missing enum members: memory_allocation_failed, processing_failed
- Replace static_assert with runtime check in memory_pool
- Update error code string mappings

* fix(build): resolve cross-platform compilation errors

- Use std::in_place_type for std::variant constructors in result_types.h
- Fix variable name conflict in test_optimization.cpp (simd_config vs scalar_cfg)
- Replace atomic struct assignment with individual member reset in ring_buffer.h

Resolves Ubuntu-GCC, Ubuntu-Clang, Windows-VS, Windows-MSYS2, and Windows-MinGW build issues.

* fix(build): resolve CI failures with variant constructors and SIMD flags

- Revert std::variant constructors to use implicit conversion
- Add AVX2 compiler flags for SIMD intrinsics support
- Support both GCC/Clang (-mavx2) and MSVC (/arch:AVX2) compilers

Fixes buffering component variant constructor issues and SIMD target mismatch errors.

* fix(result): use explicit std::in_place_type for variant constructors

- Apply std::in_place_type<T> and std::in_place_type<error_info> to all result constructors
- Ensures proper variant initialization for buffer_statistics and other types
- Fixes test_buffering_strategies.cpp compilation error

Resolves std::variant constructor ambiguity in CI builds.

* refactor(phase3): resolve fundamental compilation issues

- Simplify result<T> variant constructors for better compatibility
- Add conditional AVX2 support with compiler feature detection
- Implement copy constructor for buffer_statistics with atomic members
- Fix unused variable warnings with [[maybe_unused]] attribute
- Use index-based variant initialization with fallback to implicit conversion

Key changes:
- CMakeLists.txt: Add CheckCXXCompilerFlag for AVX2 detection
- result_types.h: Remove complex std::in_place_type usage
- buffering_strategy.h: Add explicit copy constructor for atomic structs
- simd_aggregator.h: Conditional SIMD based on CMake detection
- thread_context.h: Suppress unused structured binding warnings

This resolves cross-platform compatibility issues while maintaining
Phase 3 performance optimization features.

* fix(msvc): suppress MSVC-specific warnings for aligned structures

- Add #pragma warning(disable: 4324) for alignment padding warnings
- Mark unused parameter with [[maybe_unused]] in immediate_buffer
- Wrap pragmas with #ifdef _MSC_VER for cross-platform compatibility

Warnings suppressed:
- C4324: structure was padded due to alignment specifier (intentional for cache line optimization)
- C4100: unreferenced parameter (interface implementation requirement)

These pragmas are localized to specific classes using push/pop to maintain warning coverage elsewhere.