Adding an ACT estimate for the walks

• Improvements to the bilby implemented rwalk method

  • rwalk a new implementation which calculates an ACT to better estimate the number of steps needed

• The rwalk sample method now defaults to bilby.core.sample.dynesty.sample_rwalk_bilby_with_act which adds the maxmcmc, nact. These control the maximum number of walks, the number of ACT required before accepting a point.

• Uses the CPNest method to calculate the ACT

• Adds a guide to the documentation on using dynesty

• Updates the default vol_dec to 8 and enlarge to 1.5 which was found to improve boundary behaviour Note: during development, I experimented with adding a Jacobian and adaptive walks. I found in practise these didn't help sampling so I've removed them for simplicity.

• Updates the walks to default to 100. This is now the minimum number of steps.