docs(crc32b): add comprehensive documentation and unit tests

- Add 15 comprehensive unit tests covering:
  * Known test vectors (ISO 3309 correctness)
  * Various input sizes (1 byte to 1MB)
  * Buffer boundary conditions (256 bytes, 4KB)
  * Incremental updates and reset behavior
  * Edge cases (empty input, single byte)

- Add detailed doc comments to all public methods:
  * Struct-level documentation with examples
  * Method-level documentation with performance notes
  * Buffering strategy explanation
  * SIMD capability detection documentation

- Add feature detection documentation:
  * Performance tiers (AVX512 > SSE > Software)
  * Buffer sizing strategy (64KB for AVX512, 8KB for SSE)
  * Threshold-based flushing (256 bytes for AVX512, 4KB for SSE)
  * Architecture-specific optimizations

- Add error handling and validation:
  * Input validation (empty input handling)
  * Output buffer size validation
  * Invariant documentation
  * Edge case handling

Test Results: 15/15 passed ✅
Build Status: Successful ✅

Author: naoNao89