Fixes and improvements release

This release puts out the 4.3.* beta changes:

• Refactored Error type + Eff and Aff applicative functors

And contains a number of contributed improvements:

• Added LanguageExt Either and F# Result Converters
• Added Prism optics for manipulating Option fields
• Eq.ToEqualityComparer (Ord.ToComparer)

And a number of contributed bug fixes:

• Fix for broken Task.Cast and ValueTask.Cast
• Fix incorrect docstring for two LeftToSeq implementations.
• Fix Distinct with custom comparer (hash bug)
• Fix for SearchOptions.TopDirectoryOnly option not working
• Fix for missing implementations of FileIO (test)
• Fix for Fin.GetHashCode Throws an Exception when Fin.Succ is False

Thanks to all those who contributed. I am still super busy with other projects right now, and I don't always get to PRs as quickly as I would like, but It's always appreciated.

Any problems, please report in the Issues.