Standardize some common sampler functionality

.gitlab-ci.yml

.pre-commit-config.yaml

bilby/bilby_mcmc/sampler.py

bilby/core/sampler/__init__.py

bilby/core/sampler/base_sampler.py

bilby/core/sampler/cpnest.py

bilby/core/sampler/dnest4.py

bilby/core/sampler/dynamic_dynesty.py

bilby/core/sampler/dynesty.py

bilby/core/sampler/emcee.py

bilby/core/sampler/fake_sampler.py

bilby/core/sampler/kombine.py

bilby/core/sampler/nessai.py

bilby/core/sampler/nestle.py

bilby/core/sampler/polychord.py

bilby/core/sampler/proposal.py

bilby/core/sampler/ptemcee.py

bilby/core/sampler/ptmcmc.py

bilby/core/sampler/pymc3.py

bilby/core/sampler/pymultinest.py