Fix critical bugs and enhance security

[Eashan-H]

This PR fixes a number of critical issues identified after an audit of the code base of the FFprime project.

1. Security & Reliability

• Shell Injection Vulnerability: The code has been refactored in the get_popen utility of the file ffprime/utils/write.py.
• Safe Command Parsing: The shlex library has been integrated to safely parse the commands passed as strings.

2. Functional Bug Fixes

• Resolved Missing Imports: The import statement for the library numpy has been added to the file ffprime/utils/seminario.py.
• Variable Mismatches of potentials.py:
  • The error message has been corrected to use qa/qb instead of the incorrect q1/q2 to match the arguments.
  • The function call to compute_electrostatic_energy_with_cp has been corrected to use the alpha parameter dictionary instead of the undefined variable ref_a.
  • Several other variable mismatches have been corrected, such as the incorrect use of len(sa) instead of the irrelevant len(c6a) to compute the dispersion/repulsion energy.