DisposeAsync async enumerators in CsvWriter

[CaringDev]

fixes #2264

As an alternative we could use await using var enumerator... but this would increase the difference between the overloads.

[JoshClose]

I went with the other PR since it fixed it in all 3 places.

[CaringDev]

@JoshClose the other PR is 'better' if you favor consistency over correctness / necessity, i.e. if you want to follow These methods should all be the same very strictly (which is difficult, given async enumerators are different). As I said

As IAsyncEnumerator implements IAsyncDisposable we should unconditionally await DisposeAsync.

meaning https://github.com/JoshClose/CsvHelper/pull/2297/files#diff-e2f1fdf3fb99b4d4e65c30f3dc27dff37d93a39a2d8b1f1257f7685f3a97b5b7R638 should not check for neither IAsyncDisposable nor IDisposable and really just be https://github.com/JoshClose/CsvHelper/pull/2265/files#diff-e2f1fdf3fb99b4d4e65c30f3dc27dff37d93a39a2d8b1f1257f7685f3a97b5b7L629.
Also, enumerators implementing IAsyncDisposable but not IAsyncEnumerable should not be a thing, so the two other checks are superfluous.
The most important thing however is that the bug is fixed, so I'm happy anyways :-)

[JoshClose]

I totally read this wrong. Must have been tired. You're definitely correct here.

[CaringDev]

Hi @JoshClose

Sorry to bug you again... I think #2344 would be even better.

As an alternative we could use await using var enumerator... instead of finally but this would increase the difference between the overloads even more.