Remove fq ctx object

[Marvin-Beckmann]

Description

Previously, our ModulusPolynomialRingZq reduce used the fq_reduce from FLINT. However, the fq objects from FLINT do not support arbitrary moduli and only irreducible polynomials (in general).
In the few special cases that were important for our usecases this never occured, as we have mostly sparse polynomials and the sparse reduce works without the irreducible property.
Gennerally, this meant that the error was unnoticed.

This PR introduces its own sparse reduce function without use of FLINTs function. This removes the underlying dependency to FLINT. The method allows any modulus and any context polynomial (assuming it is monic).

Testing

• I kept all the previous tests

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
  • I have credited related sources if needed

[LPorzenheim]

Did not recalculate every changed test manually, but looked at whether they seemed reasonable.

[Marvin-Beckmann]

I made these and a few more changes that I found necessary