TimeSeries: Support `LATEST` option in queries

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/kvrocks/issues) and found no similar issues.

### Motivation

When using `TS.GET/TS.RANGE` to query a compacted time series, the `LATEST` option can be specified. This causes `TS.GET/TS.RANGE` to return the compacted value of the latest bucket, which may be a partial bucket.

Redis reference:
https://redis.io/docs/latest/commands/ts.get/

### Solution

Modify [`rangeCommon`](https://github.com/apache/kvrocks/blob/e19164f032b43c9408a5a0badf53aebeb092d97c/src/types/redis_timeseries.h#L318-L319) and [`getCommon`](https://github.com/apache/kvrocks/blob/e19164f032b43c9408a5a0badf53aebeb092d97c/src/types/redis_timeseries.h#L322-L323) to retrieve the latest bucket of source series when the latest sample is requested.

Note: Since partial aggregations are stored in `DOWNSTREAM` sub keys, we only need to fetch the last chunk of the source series to retrieve the latest bucket's aggregated value.

Refer to [`DOWNSTREAM` sub keys](https://kvrocks.apache.org/community/data-structure-on-rocksdb#downstream-sub-keys)
Refer to https://github.com/apache/kvrocks/pull/3151

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!