[client-v2] log duration in ISO-8601

[janeklb]

Motivation:

The log messages produced by Client.java (v2) include a duration, but since it is in nanoseconds it is hard to read / interpret.

for example

Query request failed after attempts: 1 - Duration: 2784541

and 2784541 is 2ms

Modification:
Log the ISO-8601 format of a duration (via Duration#toString()) when logging durations in Client.java

so above would be

Query request failed after attempts: 1 - Duration: PT0.002784541S

[windsurf-bot]

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[janeklb]

I see there is a StopWatch.java -- i could use this instead if you think it would be better (although that seems to be meant specifically for metrics as it is

public class StopWatch implements Metric {

[chernser]

Thank you, @janeklb !
The PR looks good.

[chernser]

As for StopWatch I would wait. It was added to cover very simple case.
We need to review metrics parts and build a complete observability solution.