stable-4459: cherry-pick OpenSSH security fixes

[tormath1]

In this PR, we upgrade OpenSSH to openssh-10.2_p1 to ship two security fixes on Stable:

• CVE-2025-61984
• CVE-2025-61985

Testing done

Locally emerged in the SDK:

$ sudo emerge -v openssh
...
[ebuild  N     ] virtual/zlib-1.3.1-r1:0/1::portage-stable  USE="-static-libs" 0 KiB
[ebuild     U ~] net-misc/openssh-10.2_p1::portage-stable [10.0_p1::portage-stable] USE="kerberos ssl -audit (-debug) -ldns -libedit -livecd -pam -security-key -selinux -static -test -verify-sig (-pie%*) (-xmss%)" 1929 KiB
...
$ ssh -V
OpenSSH_10.2p1, OpenSSL 3.4.2 1 Jul 2025

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.
• CI: http://localhost:8080/job/container/job/packages_all_arches/7404/cldsv/

Notes for reviewers:

• I cherry-picked relevant commits from:
  • Weekly portage-stable package updates 2025-10-13 #3366
  • Signed OS-dependent sysexts #3162 (for the virtual/zlib dependency)
• I reverted the commit "sys-kernel/coreos-modules: arm64: Enable CONFIG_FUNCTION_TRACER & CONFIG_DYNAMIC_FTRACE" that has been backported from main as it was making the /boot partition too big to pass the tests:

 index 4c92262118..81e6dec563 100644
 --- a/tmp/4459.2.3+nightly-20260210-2100-PKjZgh
 +++ b/tmp/4459.2.101+tormath1-openssh-EM1Lhr
 @@ -1,5 +1,5 @@
  File    Size  Used Avail Use% Type
 -/boot   127M   66M   61M  52% vfat
 +/boot   127M   64M   63M  51% vfat
  /usr   1016M  463M  443M  52% btrfs
  /       2.0G  576K  1.8G   1% ext4
 -SUM     3.1G  529M  2.3G  19% -
 +SUM     3.1G  527M  2.3G  19% -