ProducerStats invalid stat values

[zubchenok]

Producer latency stat values are actually in microseconds, but ProducerStats method names state that it should be milliseconds.

[zubchenok]

pulsar/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerStatsRecorderImpl.java

Line 194 in 958dcfe

ds.update(TimeUnit.NANOSECONDS.toMicros(latencyNs));