Scalar mul assign

[3pmile]

Description

This PR implements MulAssign for scalars of

• MatZ: signed and unsigned integers, Z
• PolyOverZ: signed and unsigned integers, Z
• MatPolyOverZ: signed and unsigned integers, Z, PolyOverZ
• PolyOverZq: signed and unsigned integers, Z, Zq
• PolynomialRingZq: signed and unsigned integers, Z, Zq
• MatPolynomialRingZq: signed and unsigned integers, Z, Zq, PolyOverZq, PolynomialRingZq
• PolyOverQ: signed and unsigned integers, Z, Q, f32, f64
• MatQ: signed and unsigned integers, Z, Q, f32, f64

It also implements the following DivAssign (and small fixes in Div)

• MatQ (Div + DivAssign): signed and unsigned integers, Z, Q, f32, f64
• PolyOverQ (DivAssign): signed and unsigned integers, Z, Q, f32, f64

Testing

I decided against adding a complete test coverage for all combinations of borrowed and owned, and I did not manually check all div by 0 errors that I could find, as that is not needed, and also covered in flint itself (it returns an error from there, just not a classical panic from rust, but the program is terminated regardless).

• 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
  • I have credited related sources if needed

[jnsiemer]

Nice work!
Found several small issues (almost nothing functional, mostly documentation consistency). Please take the time to check all marked bugs yourself across the documents. I've spotted some comparatively late in the review.