v0.4.1

What's changed

millsratio_d1 (−R′) and millsratio_d3 (−R‴) now accept any x (previously raised for x<0), via the reflection from R(x)+R(−x)=√(2π)·e^{x²/2}:

• R1(x) = √(2π)·(−x)·e^{x²/2} + R1(−x)
• R3(x) = √(2π)·(−x)·(x²+3)·e^{x²/2} + R3(−x)

millsratio_rel_below1 remains strict to [0,1]. Accuracy ≤1.4 eps vs mpmath down to x=−20 (conditioning-limited by e^{x²/2}); positive-x behavior unchanged.

See #2.