Add change_modulus and change_q

[jnsiemer]

Description

This PR implements...

• change_modulus
• change_q

for all non-NTT Zq datatypes.

Testing

• I added basic working examples (possibly in doc-comment)
• I added tests for large (pointer representation) values
• I triggered all possible errors in my test in every possible way
• 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)
  • The doc comments fit our style guide

[Marvin-Beckmann]

I think the current implementation is not working as intended after the mod is changed, see the respective comment