Feature request: ordering field

[sapzxc]

Hi!

I have several huge tables with primitive versioning. Actual data are in the end of table, so I prefer to sync from end of table to beginning but there are no such option.

I found orderBy($primaryKey) line but not sure it's correct thing to change this line without changing something #else.

[mrjgreen]

Its an interesting question, and I can see the value of wanting to start from the end of the table but I don't think it would be quite as simple as changing the order when fetching the values for the primary key.

The iteration through the blocks is managed here: https://github.com/mrjgreen/db-sync/blob/v3/src/DbSync.php#L96

and I think there are quite a few assumptions in here that we will be searching forwards through the table: https://github.com/mrjgreen/db-sync/blob/v3/src/Table.php#L257