Add calcPE() for Ceplecha & McCrosky PE classification

[AstroEloy]

Introduced a new calcPE() function implementing the Ceplecha & McCrosky (1976) PE end-height criterion for meteoroid structural classification.

Changes:
-Added computation of the PE parameter from end-height atmospheric density, initial mass, entry velocity, and radiant zenith angle.

• Added automatic support for WMPL Trajectory objects, deriving:
  • end-point atmospheric density from getAtmDensity_vect(),
  • zenith angle from the apparent radiant elevation,
  • initial velocity from traj.v_init.
• Added input validation for physically valid ranges (mass > 0, rho_e > 0, v_0 > 0, and cos(zangle) > 0).
• Implemented classification into structural groups I, II, IIIa, and IIIb following Ceplecha & McCrosky (1976).
• Added documentation emphasizing that the input mass should be the initial photometric mass computed using the Ceplecha & McCrosky (1976) luminous efficiency law to preserve consistency with the original calibration.