bow-shock-standofflisted

# Bow Shock Standoff Distance (aerodynamics/high-speed/bow-shock-standoff) Use when the task is estimating the detached bow-shock standoff distance on the stagnation streamline ahead of a blunt nose in supersonic and hypersonic flow: the shock stands ahead of a sphere nose or a circular cylinder leading edge rather than attaching to a sharp point, and the shock-layer thickness between the nose and the shock sets the local environment for pressure and heating trades. This leaf implements the classical Billig-form standoff correlations for gamma = 1.4 in pure Python, stdlib only: the sphere form for an axisymmetric nose and the cylinder form for a two-dimensional leading edge, both as an exponential of 1 over the freestream Mach squared. It pairs with aerodynamics/high-speed/hypersonic-flow for the force coefficients of the blunt body behind the shock and with aerodynamics/high-speed/aerodynamic-heating, whose stagnation-point flux scales with the same nose radius. The method is the standard engineering estimate for the shock-layer geometry, not a CFD replacement. ## Domain quick reference - Sphere standoff ratio (axisymmetric nose): Delta / R = 0.143 * exp(3.24 / M^2), with M the freestream Mach number, R the nose radius and Delta the standoff distance of the detached shock ahead of the stagnation point. - Cylinder standoff ratio (two-dimensional leading edge): Delta / R = 0.386 * exp(4.67 / M^2). The coefficient is about 2.7 times the sphere coefficient, so at th