Remove DnsCacheListener from DnsCache when resolver is closed

[yzfeng2020]

Motivation:

The RefreshingAddressResolver is added to the DnsCache as listener but is never removed from it when the resolver is closed. This makes the DnsCache hold a strong reference (internally, in the CopyOnWriteArrayList that stores all the listeners) of it even when the resolver is closed, which may cause memory leak if the DnsCache is a global one and lives for the lifetime of the JVM.

Modifications:

• Removes the DnsCacheListener from the DnsCache to make it eligible for GC.

Result:

• Closes Possible memory leak wrt RefreshingAddressResolver #6173.
• When the resolver is closed, the DnsCache no longer stores it in the list and hence no longer holds a reference of it.

[github-actions]

🔍 Build Scan® (commit: 5dfc31c)

Job name	Status	Build Scan®
build-ubicloud-standard-16-jdk-8	✅	https://ge.armeria.dev/s/liu2ydst3dshq
build-ubicloud-standard-16-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/65fnsl3iew3xe
build-ubicloud-standard-16-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/isgknf3c4wmwo
build-ubicloud-standard-16-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/r44dsm4foo7nc
build-ubicloud-standard-16-jdk-17-leak	✅	https://ge.armeria.dev/s/uo2jvcn5yovru
build-ubicloud-standard-16-jdk-11	✅	https://ge.armeria.dev/s/3kqyfonnbgkry
build-macos-latest-jdk-21	✅	https://ge.armeria.dev/s/x2yimozogrqly

[trustin]

Thanks a lot for fixing this, @yzfeng2020! I left one nit, but it looks great! 🙇

[minwoox]

Thanks!