fix(build): format runAfterProductionCompile duration as human-readable time (#89232)
This change should unifiy the runAfterProductionCompile output to follow
the same style as other times printed in the build logs.
Currently build logs look like
```
✓ Compiled successfully in 89s
Running next.config.js provided runAfterProductionCompile ...
✓ Finished writing to filesystem cache in 18.5s
✓ Completed runAfterProductionCompile in 36134ms
Skipping validation of types
```
I hope they will now look like
```
✓ Compiled successfully in 89s
Running next.config.js provided runAfterProductionCompile ...
✓ Finished writing to filesystem cache in 18.5s
✓ Completed runAfterProductionCompile in 36.1s
Skipping validation of types
```
(and yes i know 36s is shameful thats my next problem but this irked me
enough to want the build output looking nicer ahhaha)
It feels like adding a test for this would be semi counter productive
without basically ending up adding sleeps and then in reality its
testing more the logic of `durationToStringWithNanoseconds`.