fix/checking-memtable-empty-and-stats:
- **Refactor timestamp updates**: Simplified timestamp range updates in `PartitionTreeMemtable` and `TimeSeriesMemtable` by replacing `update_timestamp_range` with `fetch_max` and `fetch_min` methods for `max_timestamp` and `min_timestamp`.
- Affected files: `partition_tree.rs`, `time_series.rs`
- **Remove unused code**: Deleted the `update_timestamp_range` method from `WriteMetrics` and removed unnecessary imports.
- Affected file: `stats.rs`
- **Optimize memtable filtering**: Streamlined the check for empty memtables in `ScanRegion` by directly using `time_range`.
- Affected file: `scan_region.rs`
(cherry picked from commit 1a517ec8ac)