v0.5.0: Tune estimated thresholds via accuracy search

[GeEom]

Saturation semantics for total functions, improved angle reduction, and threshold tuning

Saturation Over Errors:

• Removed Error::Overflow variant entirely
• Total functions (exp, pow2, sinh, cosh, tan) now saturate deterministically
• exp/pow2: Saturate to T::MAX for large positive inputs, zero for large negative
• sinh: Saturates to T::MAX or T::MIN based on sign
• cosh/tan: Saturate to T::MAX near poles/overflow

sin/cos Large Angle Fix:

• Replaced iterative angle reduction loop with direct quotient computation
• Old approach hit iteration limits for angles near I16F16::MAX
• New approach: reduced = angle - round(angle/2π) * 2π

Threshold Tuning:

• Taylor/CORDIC crossover thresholds optimized via golden section search
• High-precision (≥24 frac bits): 0.05 → 0.1366
• Low-precision (<24 frac bits): 0.1 → 0.2776

Documentation & Cleanup:

• Added saturation threshold tables to README
• Comprehensive doc comments for overflow behavior
• Made NormalizedLnArg and related helpers crate-private

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/ops/circular.rs	80.00%	2 Missing ⚠️

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