ActiveRecordBatchEnumerator#each should rewind at the end

[etiennebarrie]

While looking at the code for #94, I found out that our each is a bit surprising since it remembers its state (because it keeps the cursor). Calling each again on a enumerator doesn't iterate again, it doesn't yield.

Calling each twice in a row should yield all the batches again, like an Array or any Enumerator does:

results = []
array = [1, 2]
array.each { |i| results << i }
array.each { |i| results << i }
results # => [1, 2, 1, 2]

I tested that by creating an enumerator with a cursor, and checking that we only get the remaining batches, twice. At first I reset the cursor entirely, but that would cause 4 batches first, then the full 5 batches on the second call to each, which was also an unexpected behavior. I don't really expect users to use this a lot but it's more correct at very little cost so worth it!

[adrianna-chang-shopify]

Yeah, I had the feeling having an enum with state tracked inside @cursor was going to throw something off. 😆 Since we've bothered to make this a proper Ruby Enumerator it definitely makes sense to me to make this correct and rewind properly based on the cursor we first built the enumerator with. Nice catch! 🚀