This function calculates several summary statistics for time series data. The function calculates the following metrics for all key combinations:
start: Start date (or date-time)end: End date (or date-time)n_obs: Number of observations per time seriesn_missing: Number of missing values (NAs)pct_missing: Percentage rate of missing valuesn_zeros: Number of zero valuespct_zeros: Percentage rate of zero values