MNT: change bilby MCMC to use glasflow instead of nflows

Closes #729 (closed)

I also took this chance to switch the tests to use pytest-requires which will mark tests that require glasflow as skipped rather than passing when it is not installed.

This will also require a change to the images, so we should be slighlty careful when merging this.

added 10-100 lines Sampling labels

@gregory.ashton are you okay with this change? I suggested it earlier as glasflow is also used in nessai and is available via conda.

changed milestone to %2.4.x

approved this merge request

@colm.talbot just as a note I am happy and approved it.

approved this merge request

added 9 commits

• a191e972...49c1c393 - 4 commits from branch lscsoft:master
• eb0b1afa - MAINT: use glasflow.nflows instead of nflows
• 534da2b0 - TST: optionally skip tests that require glasflow
• e5b43593 - BLD: change nflows dependency for glasflow
• f5754275 - CI: add pytest-requires to enviroment
• 5d9ea8ac - BLD: add pytest-requires to optional requirements

Compare with previous version

added 6 commits

• e008142c - 1 commit from branch lscsoft:master
• df3aafce - MAINT: use glasflow.nflows instead of nflows
• 9debf63b - TST: optionally skip tests that require glasflow
• f28683e2 - BLD: change nflows dependency for glasflow
• 67aa195d - CI: add pytest-requires to enviroment
• 014df2ed - BLD: add pytest-requires to optional requirements

Compare with previous version

merged

changed milestone to %2.3.0