Unresolved IPv6 InetSocketAddress serialized without brackets, losing port on round-trip #6185

(reported by @renechoi in #6125 — fix to be implemented independently as the original PR was closed without a CLA)

InetSocketAddressSerializer writes values as host + ":" + port. For a resolved address it takes the host part from InetAddress.toString() and brackets IPv6 literals, so output looks like "[2001:db8::1]:443". For an unresolved address there is no InetAddress, so it falls back to getHostName() and writes an IPv6 literal bare:

InetSocketAddress.createUnresolved("2001:db8::1", 443)
// serialized as "2001:db8::1:443"

The trailing :443 is indistinguishable from another hextet, so the port cannot be recovered on deserialization.

This has become more visible since #5951: deserialization now always constructs unresolved addresses via InetSocketAddress.createUnresolved(), so a bare IPv6 address value read by Jackson no longer survives a round-trip — on re-serialization the port gets appended bare, and the next read absorbs it into the host name.

Expected: the unresolved branch should bracket IPv6 literals the same way the resolved branch already does, e.g. "[2001:db8::1]:443". Host names that are already bracketed (which is what the deserializer stores for "[...]:port" input) must not be bracketed twice.

Applies to 2.x (2.18+) and 3.x; existing JDKTypeSerializationTest.testInetSocketAddress() covers the unresolved form only for IPv4 and host names.