Arithmetic between Z and f64/f32

[jnsiemer]

Description

This PR implements...

• missing cross-type arithmetic between Z and f64 / f32

Testing

• I included tests for all reasonable edge cases

Checklist:

• I have performed a self-review of my own code
  • The code provides good readability and maintainability s.t. it fulfills best practices like talking code, modularity, ...
    • The chosen implementation is not more complex than it has to be
  • My code should work as intended and no side effects occur (e.g. memory leaks)