Tachyon 0.7.0 Optimizations

[google-labs-jules]

Implemented comprehensive performance optimizations for Tachyon JSON library:

1. Small File Optimization (<1KB):
   • Implemented Small Buffer Optimization (SBO) in Context and Document to bypass heap allocations.
   • Added find_key_direct for lazy scanning of keys without generating full bitmask.
   • Optimized as_string to use direct scanning for small files.
   • Added TACHYON_FORCE_INLINE to hot paths.
2. Large File Optimization (250MB+):
   • Implemented branchless escape character handling in compute_structural_mask_avx2 using bitwise logic.
   • Improved validate_utf8 with AVX2 fast scan for ASCII and lengths (hybrid approach).
   • Added hardware prefetching hints (_mm_prefetch).
3. API & Cleanup:
   • Upgraded to version 0.7.0 "QUASAR".
   • Removed Mode::Apex enum.
   • Implemented template-based Compile-Time Validation Toggle (Context<bool>).
   • Fixed unaligned store crash in AVX2 code (_mm_storeu_si128).
4. Verification:
   • Created benchmark_optimization.cpp and generate_canada_json.py.
   • Verified correctness with test_tachyon.cpp.

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PR created automatically by Jules for task 6697665385524651958 started by @wilkolbrzym-coder

[google-labs-jules]

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