Add IEEE 754 special value (+/-Inf, +/-NaN) support and tests to Highway math functions

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Add IEEE 754 special value (+/-Inf, +/-NaN) support and tests to Highway math functions

This change ensures that Highway math functions conform to IEEE 754 / C11 Annex F specifications for special inputs (+/-Inf, +/-NaN) and adds comprehensive unit tests covering these cases:

• Erf: Added explicit NaN handling to prevent x86 minps/minpd semantics from clamping NaN to +1.0 (+/-Inf handled implicitly via range clamping).
• Exp / Exp2: Added explicit handling for +Inf / overflow (preventing range reduction arithmetic cancellation into NaN) and NaN (preventing underflow flush to +0.0).
• Log / Log2 / Log10: Added explicit handling for negative inputs (NaN), +/-0 (-Inf), +Inf (+Inf), and NaN (NaN).
• Tanh / Expm1 / Log1p: Verified that special inputs (+/-Inf, +/-NaN) are handled implicitly by the underlying arithmetic and range reduction without requiring extra checks.
• Tests: Added TestSpecialValues in math_test.cc and TestTanhSpecialValues in math_hyper_test.cc covering float32 and float64 across all vector widths.

Performance Impact:

• Tanh, Expm1, Log1p: 0% overhead (0 instructions added).
• Erf: Negligible overhead (1 compare + 1 blend).
• Exp / Exp2: ~2-4% throughput overhead (2 compares + 2 blends).
• Log / Log2 / Log10: ~3-5% throughput overhead (4 compares + 4 blends).
  Critical-path latency impact is negligible (0-1 cycle) on superscalar architectures because comparison masks depend solely on the input register and are evaluated by out-of-order execution in parallel with the arithmetic pipeline. Workloads requiring maximum throughput on finite inputs can continue using the Fast* variants (e.g., FastExp, FastLog).