Returns how many tokens per minute each provider processed, per time bucket, over the date range. The bucket size grows with the length of the range, from a minute to a month; for buckets wider than a minute the figure is the average over the minutes of the bucket that had calls. For one figure per group over the whole period, a far smaller answer over a long date range, use get_tokens_per_minute_aggregated, which does not take providers, tokenType.