refactor: remove LoadCheckpointError and ApplyLogError

[roeap]

Description

This PR removes LoadCheckpointError and ApplyLogError as well as moves some more checkpoint related functions into the checkpoint module.

Aside from cleaning up errors, this moves us a little bit closer to isolating log handling related logic in preparation for some upcoming work.

Related Issue(s)

part of: #1136

[roeap]

@cmackenzie1 - do you have an opinion on the general direction where this is headed? I.e. the way I see it right now, we would end up with a single top level error DeltaError, Underneath that we would have one level more of delta specific error like ProtocolError or CommitConflictError, where we try to give specific the user may wnat to react on. Things like object store errors etc would still be surfaced similar to what we do now.

and everyting in delta-rs just returns a DeltaError ...

[cmackenzie1]

and everyting in delta-rs just returns a DeltaError ...

@roeap I think that sounds great. Right now there are a few things that return different errors so you can't use ? if they are in the same scope.

Is there the possibility to create a class of errors Retryable? Things for transient errors like 5xx from object stores?

[wjones127]

All seems reasonable :)