fix: dispose enumerator in CsvWriter.WriteRecordsAsync

[vchirikov]

We should check enumerator with IAsyncDisposable too.

p.s. A bit better version of #2265

Closes: #2264

[CaringDev]

Why do you think this is better than #2265 ? IMO:

1. if we get a synchronous enumerator, we should Dispose synchronously. Or do you know of any counterexample?
2. if we get an asynchronous enumerator, no check is needed, just use DisposeAsync

[vchirikov]

@CaringDev at least because:

		// These methods should all be the same;
		// - WriteRecordsAsync(IEnumerable records)
		// - WriteRecordsAsync<T>(IEnumerable<T> records)
		// - WriteRecordsAsync<T>(IAsyncEnumerable<T> records)

but #2265 changes only one overload. And also you don't know about implementation of enumerator, so it might implement IAsyncDisposable or IDisposable. Library code should support both, imho.