update to use pymbar >= 4.0

[orbeckst]

With the new version of pymbar, some names changed. These need to be fixed.

• fix names
• bump requirement to pymbar >= 4.0 (same as alchemlyb)
• alchemlyb >= 2

Example:

 File "/Users/oliver/anaconda3/envs/mdpow310/lib/python3.10/site-packages/mdpow/fep.py", line 157, in <module>
    from pymbar.timeseries import (statisticalInefficiency,
ImportError: cannot import name 'statisticalInefficiency' from 'pymbar.timeseries' (/Users/oliver/anaconda3/envs/mdpow310/lib/python3.10/site-packages/pymbar/timeseries.py)

[orbeckst]

@VOD555 could you fix this?

Then we can also increase the alchemlyb requirement to >= 2 (setup.py and other installation files).