Improve code coverage

[olexandr-konovalov]

• [x] ExtSSPAndDim for trivial group
• [x] ExtremelyStrongShodaPairs
• [x] StShodaPairs

• [x] IsNormallyMonomial to cover normally monomial but non metabelian https://github.com/gap-packages/wedderga/blob/81068c1c6fa8b2aea43197204dde78d0107423ec/lib/ExtremeSSPs.gi#L180

  Update: added more files requiring better code coverage:

• [ ] idempot.gi
• [ ] crossed.gi
• [ ] auxiliar.gi
• [ ] others.gi
• [ ] main.gi
• [ ] div-alg.gi
• [ ] BW.gi