Use newCachedTreadPool() instead of newSingleThreadExecutor() in InetUtils

[stsypanov]

See #1364

[OlgaMaciaszek]

Fixes gh-1364.

[OlgaMaciaszek]

Hi @stsypanov. Thanks for adding the PR. However, could you please submit the change against the 4.1.x branch instead? Also, please add your full name and last name with the @author tag to the class Javadoc and update the date in the license comment to 2012-2024

[stsypanov]

@OlgaMaciaszek done! I've also removed TODO comment as the executor is shut down in close() method and shutting it down before calling close() doesn't make sence if we use newCachedThreadPool().

[OlgaMaciaszek]

Thanks @stsypanov. LGTM.