gh-40991: refresh our Macaulay2 interface
    
so that

- there is a global "optional macaulay2" doctest marker
- almost all doctests pass, although there remains an issue about
ChainComplex
- conversion of polynomials uses a dict rather than a string
- conversion of rationals use numerator / denominator rather than a
string

Note that the conversion of ChainComplexes works, there is only a
failure when running "sage -t"

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #40991
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager