Calculate the signed deviation from an exact aspect.
Parameters
transitLongitude: number
Current longitude of transiting body
natalLongitude: number
Longitude of natal point
aspectAngle: number
Target aspect angle (0, 60, 90, 120, 180)
Returns number
Signed deviation from exact (negative = before exact, positive = after)
Remarks
This is used by binary search to detect sign changes that indicate
the exact aspect crossing. The sign of the deviation tells us which
side of exact we are on.
Calculate the signed deviation from an exact aspect.