[Bug] Mismatch of ProducerStats/ConsumerStats interface description and implementation

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Version

2.11.0 and above

### Minimal reproduce step

1. Create a non-partitioned topic
2. Create a producer with the default 60sec statsInterval that can publish messages to topic in step 1
3. Publish 1 message every 10 sec, and 20 messages in total
4. Fetch the producer stats every 20sec by querying `getStats()` method and print out values of [getNumMsgsSent()](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java#L39C10-L39C24) and [getTotalMsgsSent()](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java#L99) in [ProducerStats.java](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java)
5. Check the printed logs

### What did you expect to see?

Both `getNumMsgsSent()` and `getTotalMsgsSent()` should be constant values during each statsInterval(60sec) per the [description](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java#L30), as all stats are referring to the last recording period(last stats interval)

### What did you see instead?

- `getNumMsgsSent()` is actually the number of messages published in the current interval, **NOT** the last interval
- `getNumMsgsSent()` is being updated within the interval

Implementation also indicates current interval
[ProducerStatsRecorderImpl.java](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerStatsRecorderImpl.java#L141-L144)

### Anything else?

Client stats that are referring to current in progress interval
- [ProducerStats](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java#L36-L54)
- [ConsumerStats (part-1)](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ConsumerStats.java#L40-L45)
- [ConsumerStats (part-2)](https://github.com/apache/pulsar/blob/v3.1.0/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ConsumerStats.java#L60-L75)

Is there any ongoing plan to fix the documentation or the implementation ?

### Are you willing to submit a PR?

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

Start with pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerStats.java and ConsumerStats.java, then compare their descriptions with pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerStatsRecorderImpl.java. Determine whether the documented or implemented stats-interval behavior is intended, and align the affected interfaces and implementation so the current versus previous interval is unambiguous.

Written by the indexing model from the issue text.