Function radiusVector

radiusVector(
    eccentricAnomaly: number,
    semiMajorAxis: number,
    eccentricity: number,
): number
Calculates the radius vector (distance from focus) given eccentric anomaly.
Parameters
- eccentricAnomaly: number
  Eccentric anomaly E in degrees
- semiMajorAxis: number
  Semi-major axis a (in any unit, typically AU)
- eccentricity: number
  Orbital eccentricity e
Returns number
Distance r from the focus (in same units as semiMajorAxis)
Remarks
r = a · (1 - e·cos(E))

At perihelion (E = 0°): r = a(1-e) At aphelion (E = 180°): r = a(1+e)
Example
```
// Earth at E = 0° (perihelion)
const r = radiusVector(0, 1.0, 0.0167);
// r ≈ 0.9833 AU
```
Source
Meeus, "Astronomical Algorithms", Eq. 30.2, p. 195
- Defined in ephemeris/utils/kepler.ts:210